I recently have gone thru the traditional to lightweight backpacker transformation. Actually I bought a bunch of gear and thought that I was as strong as ox. I don't even want to go into the details of what I brought… Okay I'll mention a few things: a whisperlite, a 2L and 1.5L stainless pot, blue jeans, a 8oz petzl duo headlamp and a minimaglite (4oz), eggs (and egg carrier), camelbak bladder and nalgene, 2 4oz knives, teva sandals and way too much food. Even though I was strong as an ox, I was exhausted after 5 miles and 2000' of elevation gain. It was a great trip however, what an adventure. The pack probably weighed 60lbs total, but it felt like 100lbs when I packed out. Now I'm at a much more reasonable base weight of 15lbs for the PCT.
The first step is to make a list of everything that you bring and start getting rid of stuff you don't need or is redundant. This has been mentioned previously.
1) I like the previous poster's comments about trying different shelters with MYOG. I tried a tarp and didn't like it. I also wouldn't like a bivy, but may be interested in a hammock someday. I'm most comfortable in my tarptent (2lbs).
2) I had no idea that I would enjoy an alcohol stove so much. Your friends/family will think you're crazy, but they work so well. I use the hiknakd stove (reviewed here at BPL and available on ebay).
3) Water filtration is another area that you can save some weight. I haven't switched over from a filter yet, but I'm looking at some of the different options. Some great articles/threads on here about the effectiveness of different methods. I do like the gravity filter at ULA.
4) If you're cooking solo, you really only need a .9L (maybe even smaller) pot. You can a wal-mart grease pot or a titanium pot at around 5 oz. A pot cozy might make your stove more efficient and use less fuel (for example one of the anti-gravity gear cozies).
5) Clothing is one of the toughest systems to get perfect at minimal weight. Cotton is a big no-no. I still have 5.5 lbs of clothing (including what I'm wearing, excluding shoes).
I have a T-shirt, long sleeve sun shirt (also for bugs), light fleece (9oz), wind shirt, orange poncho (2 oz) and a used cocoon (thanks to a BPL member). I have shorts, sun pants, light fleece pants (9 oz) and wind pants. To round out the list I have a stocking hat, powerstretch gloves (1.5 oz), BPL sun hat, bandana, 2 prs socks, headnet and an umbrella (for the sun).
I could easily take a 1-2 lbs out. T-shirt and shorts (1/2 lb combined) aren't really needed, but can be used for hiking, sleeping, and swimming. And I probably have a little too much insulation but I'll just have a really comfortable pillow if not needed.
7) You can probably find a trail runner to work for you, but make sure that it works for you. The soloman XA series fits me real well. I portaged a 50lb canoe with my trail runners and they are great since they drain water so well. But carrying a canoe might be pushing the limit on trail runners depending on the individual and the terrain.
8) You don't need a lot of knife. I have a 2" gerber LST at .6oz.
9) It may be difficult to go low-tech and use a plain water bottle (like aquafina or gatorade), but they are definitely the most weight effective. The nalgenes and hydration bladders are quite heavy.
10) Choose your gadgets wisely. There are lots of fun toys out there that can add up quickly in weight. And batteries are also quite heavy.
11) You can try a foam pad to replace a thermarest style pad, but it's not for everyone. I find myself comfortable on the 3.7oz 3 section pad from gossamer gear with my pack under my legs.
At the end of all of this you can select a nice 2-3lb 50-60L pack (or even smaller).
These are just some of my details on my transition from traditional to lightweight backpacking. Alot of this stuff you probably already know, but I did not. There are many good articles on BPL (and other websites) to get info on some of the different items and techniques that can be used to lighten your load.
Also be sure to visit some of the lightweight manufacturers websites to see what items are available. The BPL store, ULA-equipment, gossamer gear, anti-gravity gear, and montbell are some of my favorites. And some of these sites have several links to other similar sites.