Less is More
For those of you who have always thought of touring in terms of grinding your way up hills with raw power, there's good news. There's another approach to bicycle touring - ultra lightweight. By carrying less weight, you can greatly extend your range and make pedalling up hills a lot easier. This means racking up a lot more miles (if you're a mileage freak) and seeing a lot more new territory (if you're a typical tourist) in the limited time you have. You may even be willing to tackle more elevation or longer distances than usual, opening up a host of dramatic new routes. Of course, all this means taking a fresh look at your equipment, gear and supplies. And remember, when it comes to the cost of gear, less is always more!
The Bicycle
In touring, the emphasis has traditionally been on strength, not speed, with steel frames and muscular racks front and back.
In particular, smaller, stronger wheels with a high spoke count and wide, thick tires have served to support the extra load. Ultra lightweight touring allows the use of lighter, stiffer, faster bikes without heavy duty racks, and you can save more than a pound apiece on wheels and tires alone. With the lighter load, you can use larger, lighter wheels with fewer spokes and 1 1/8 " (or even 1") high-pressure tires, reducing weight and usually increasing speed. Downside: if you go off-road, these advantages may become disadvantages again.
Another good reason to shave weight on the wheels and tires is that rotating mass offers more inertia than the same mass packed in your pannier, and it takes more energy to move it down the road. Pay close attention to the weight of tires and tubes when you buy - the differences among them can be quite surprising. Downside: the lightest tires are racing tires, which won't give you the puncture protection you'd like on a tour - the optimum choice is probably something a bit heavier with better protection.
If you're looking for just the right bike, lightweight touring bikes, cyclocross bikes and sturdier road bikes are all good candidates.
Bike Gear
Base Gear Weight
One concept that's important to grasp is that of Base Gear Weight. This is the combined weight of gear and equipment and accessories you carry on your bike (including the clothes you wear while riding) - everything except consumables like food and water, which will fluctuate during your tour. This is really the number to watch as you downsize your load. A 15 pound limit is considered good by ultralight riders.
Racks
Racks can weigh from 1 to 2.5 pounds, and touring racks are usually at the heavy end of that scale. With less weight to carry, you can use lighter racks. You can conceivably do without racks altogether by strapping gear directly to the bike frame: suspended from saddles, from the middle of the frame or from the handlebars.
If your bags are light enough and tied down well enough to keep from swinging too much, this could be a satisfactory solution. Downside: your gear may pack too high on the bike, keeping your center of gravity high and making the bike unstable and hard to handle. If you do use 
racks, load heavy items in the front where it's low, put lighter, bulkier items on the rear rack.
Luggage
Panniers weigh 2 to 4 pounds apiece. Stuff sacks weigh about an ounce. Carrying gear in stuff sacks tied directly to your rack can save a lot of weight. For waterproofing, use a garbage bag inside the stuff sack. Downside: access to gear is more difficult, attachment may be tricky and garbage bags may not be as waterproof as you thought.
Carousel Design Works and Relevate Designs offer soft luggage systems designed specifically for lightweight bike touring which eliminate racks by using the space within the frame, strapping directly to the frame or bars.
Accessories
Put new batteries in all your electronic gear before you leave - you'll feel better about not taking extra batteries. And do you really need all those fancy gizmos on your bars? Think hard about what's really necessary.
What to Pack
If you're going ultra lightweight, you need to rethink what is essential. Here's a suggested ultra lightweight packing list. As they say in backpacking, "take care of the ounces and the pounds will take care of themselves."
Shelter 
You may have thought that 3-season packpacking tent was pretty light,but there are even more lightweight options. You can reduce that tent's 6 pounds to about 24 ounces by using a light silnylon tarp with poles and stakes and a groundcloth instead. A lightweight tent rainfly and footprint (without the tent itself - called "fast-fly" or "fly & floor" configuration) will do much the same. 
Tossing in a bug net to keep you bite-free will add perhaps an ounce. Even full tents are becoming lighter; the Big Agnes Fly Creek, for example, weighs in at 35 ounces (poles & fly included) and offers 22 square feet internally and 5 square feet of vestibule. Ditch the 3 pound sleeping bag and use a down quilt to lose 2 more pounds. Instead of a cushy full length sleeping pad, use a thin torso pad and you'll go from 2 pounds to about 8 ounces. Depending on where you're camping, you can make like the pioneers and use pine boughs or other vegetation as bedding under your groundcloth. Downside: you're going to be less comfortable in camp. If you happen to get freaky weather, you could be a lot less comfortable - you're cutting the margins pretty thin.
Cooking Gear
First of all, you'll want to think simple. Carry one titanium cooking pot instead of two and stick to one-pot meals - if you can forego those morning pancakes, there's no need for a frying pan or spatula. A single Lexan spoon or spork for both cooking and eating will save several ounces over a metal knife, fork and spoon plus cooking utensil. You may love your white gas burning Coleman camping stove, but it's 2 pounds with fuel, and you'll carry refills in a heavy metal canister - an ultralight unit like the MSR Pocket Rocket with isobutane cannister is 11 ounces. Instead of a filtered pump for water, take a small bottle of chemical purifier such as Klearwater - it'll weigh less and pack smaller. Don't put those waterproof matches in that expensive watertight metal cylinder - use a plastic baggie. Downside: lightweight gear is expensive gear.
Personals
Lose that 3 ounce metal mirror and pick up a 1/2 ounce plastic one. Cut the handle down on your toothbrush. Eliminate as much original packaging as you can - it's heavy and it takes up space; instead of throwing in a full bottle of aspirin, put 20 capsules in a lightweight plastic baggie. Use a microfiber washcloth instead of the old terrycloth one - it's lighter, packs smaller, dries quicker and doubles as a bandana in town. Take a plastic comb instead of a hairbrush. Don't take full rolls of toilet paper or duct tape - unwind them from the cores and rewind just what you think you'll need around a pencil (plus you can write with the pencil). Reexamine your need for personal electronics - they pack a lot of weight in a very little space. Get the picture? If you can save just one ounce each on sixteen little things like these, you'll save a full pound and never notice the functional difference! Downside: none.
Clothing
Clothes are a good source of weight savings. For example, a down vest compresses better and weighs less than comparable fleece. Rain pants can vary in weight from 5 to 16 ounces. From socks to hat, weigh each item and consider its value and whether you can get multiple uses from it. Riding clothes can also double as off-bike clothes if you choose well. Downside: you may get to smell and feel funky in a few days if you don't have a chance for a laundry stop.
Tools 
Tools, particularly metal ones, pile up the ounces pretty quickly. Trade your old steel levers for small plastic ones. Look for a lightweight pump. Carry only the tools you'll likely need and consider a multitool over several individual tools. One Fiberfix Kevlar spoke, which will fit anything, is lighter and more compact than carrying extra spokes for all the wheels in your party. Downside: the tool you leave home will be the one tool you really need on the tour. I guarantee it.
Food
Taking significant weight out of your food really requires a paradigm shift in thinking. What really matters, when you get down to the finer points, is not grams of food, but calories per gram (or calorie-to-weight ratio) of food. Dried and freeze dried food seem sensible at first, because they provide more grams (after hydrating) of food served for their dry weight than other kinds of traditional camping food. But calories, not grams, are the measure of how much energy food will give you. And the foods with the most calories per gram are fats and oils. These provide about 9 calories per gram, while nuts and nut butters yield 6 to 7 calories per gram. Meat and bean protiens offer about 4 calories per gram, as do carbohydrates in pasta and rice, which have to be hydrated and cooked, requiring pots, pans and utensils which add weight. Bottom line: the most weight efficient foods are those with high fats and oils. Downside: (this is a big one) specialists in nutrition for athletes will tell you that when your body is working it really needs carbohydrates more then fats. Fats require lots of energy to digest - energy which could be otherwise directed to pedalling. Going heavy on fats, oils and protiens also causes many bikers digestive discomfort during the ride. This is a case of weight efficiency being in conflict with eating efficiency. Another downside: after pedalling hard all day and lying on cold, hard ground in a strange place, traditional comfort foods are a welcome comfort, indeed!
Double Up
One sure-fire strategy for losing weight is to get more use from the same gear.
A bicycle headlight also makes a good camp light. MTB style shoes with recessed cleats also make good off-bike footwear, eliminating the need for a second pair of heavy shoes (if you really need extras, use flip-flops). A knife on your multitool eliminates the need for carrying a jacknife. A cyclocomputer with a watch function means you don't need a wristwatch. Baggy riding shorts and technical T shirts double as off-bike wear. One container of biodegradable soap can serve to wash food and dishes, bathe bodies, shave and brush teeth. You can find much more if you look. Downside: none, really.
Minimum Impact Camping
Because of the enormous pressure on the little remaining wilderness we have, it is our responsibilty to leave it as unmarked by our presence as possible. Leave no footprint. This is your ethical obligation to your children and grandchildren.
New Frontiers
Ultra lightweight riding can open up new horizons for you, but it's better for short trips than long hauls off-road or into third world countries where spare parts, tools and supplies are hard to get. If you're going there, you'd better rely on traditional methods - the longer you ride, the more likely it is you'll need something you don't have.
