For those of you who are interested in this hobby I would definitely suggest reading Lightweight Backpacking and Camping, it is a pretty nice survey of techniques and gear used by notable lightweight hikers.
I went on a weekend trip to Lost Maples and after a long day I found myself descending a rather steep hill with a 40 pound pack (base weight: 24.4 lbs), and the next day my knees were pretty sore. The pain didn’t go away for a week. It was then that I decided it was time to address the weight of my pack. I borrowed a scale from the instrumentation lab at school and set out to weigh everything in my pack, I input the results into a spreadsheet.
Then I looked at what I carried that I didn’t use, immediately I found a big group things that I could leave at home: my multitool, all that extra parachute cord, the climbing carabiners, and a score of container type things. I would typically carry a dromedary bag and four nalgene bottles; forget that, all I need is the dromedary bag and one nalgene bottle. Also, not carrying all those containers reduces the amount of water I feel compelled to carry (weighing in at 34 ounces per liter, water weight is an essential reduction), I'll address hydration below.
So, I'm only allowing myself 5 liters of water capacity, no big deal, if I bring along some water treatment I can just fill up at streams along the way. Five liters is actually a bit more than is necessary, the hardcore ultralighters will carry under 3 liters typically (based on availability of water).
The next step was to look at things I’ve been carrying that weigh too much. Back to hydration: A nalgene weighs upwards of 6 ounces, whereas a collapsible Platypus weighs 0.88 ounces. My high tech stove (MSR Fusion) is really nice—and it boils water really quickly—but it weights about 20 ounces (including the pot and lid, excluding fuel), a homemade alcohol stove weighs next to nothing (0.4 ounces), plus it is essentially free. Add a lightweight pot (or in my case a tiny bowl), a windscreen, and a lightweight spork, and you have a complete cooking kit that weights well under half a pound. For multi-person trips (4 people or so), where everybody will be boiling water (exclusively) to cook I will carry the heavier stove—or split it amongst several hikers—to take advantage of its fast boil time and wind resistance.
I also decided to do away with the tent. Instead I use a homemade tarp (which is also a poncho), if it is raining while I’m bedding down I just stay under it (you can cook under there too). You can purchase Sil-Nylon which weights 1.3 ounces per square yard for a reasonable price from Quest Outfitters and get to sewing (you can get everything else you need from quest too). Some folks will get themselves a TYVEK groundsheet, but that stuff will wear out pretty quickly and it is quite noisy. I'm still carrying a standard ground cover, but I'm working on a way to make that multi-use too; once the design is complete I'll post it here.
My decision to use a tarp requires some extra gear: trekking poles, to act as the support. This little expense turned out to be a real blessing, they allow the hiker to take some of the stress off the knees, and let the arms do some of the work. All said, the trekking poles, tarp, and rigging weight just over what the body of my tent weighs alone (without the fly and poles). And the use of the poncho as rain gear allows be to get rid of the weighty rain gear.
With the reduced weight of the stuff going in the pack I can justify using a pack with less support—one that doesn't weigh 5 pounds—I plan to buy or make a pack weighing just over one pound. This pack will utilize the sleeping pad a padding and load transfer.
Also, with the reduced weight I can finally justify bringing along some of the things I used to leave behind due to the heavy weight… like a first aid and survival kit (it wasn’t till I picked up on ultralighting that I realized how light one of those could be).
Earlier I mentioned those heavy containers (toiletry bag, utensil bag). If you pick up a few ALOKSAKs you can keep all your stuff organized, visible, and waterproof, at a minimal weight cost (they are pretty cheap yet durable).