You aren't lightweight backpacking if you are carrying twenty-five pounds for a summer weekend. I invent these standards, but I try to be reasonable. I backpack with less than fifteen pounds total weight for a weekend trip. With a few new pieces of gear, and a little knowledge, you can probably carry less than twenty pounds for a three-day trip, and less than thirty for a week-long trip.
Start by throwing out those pack weight/body weight formulas. Learn the principles of lightweight backpacking, and you'll never be close to what they say you can carry anyhow. And who wants to carry 25% of their body weight down the trail? The question to ask is "How much do I need to carry to be safe and comfortable?"
Lightweight Backpacking Isn't Masochistic
The biggest reason for lightweight or ultralight backpacking is to enjoy the trip more. I don't leave crucial things behind or otherwise make myself miserable, just so I can call it lightweight backpacking.
Here's a good rule: Go as light as you can without sacrificing things that are most important to you (safety items, a good book, a bottle of rum?). It's not about giving things up. It's about carefully choosing what you really need to have an enjoyable, safe trip, AND replacing heavier things with lighter things.
For example, if you really need an inflatable pad, get rid of that 2-pounder and buy one of the new 13-ouncers. My down sleeping bag weighs 17 ounces and has kept me warmer than any 3 or 4 pound bag I've had. If you replace items one-by-one with lighter alternatives, you can eventually cut your packweight by half or more.
Start by setting aside your lightest sweater, socks, hat, etc. Then, when you can afford to, buy one of the big three (pack, tent, bag) because this is where you'll save the most weight. Of course, going light can be expensive, but I've gone 110 miles in seven days (no blisters) with running shoes, so it doesn't have to be.
How Much Weight?
With proper equipment and skills, you probably can be comfortable and safe with twenty pounds on your back for the weekend. Watch yourself on your next hike. What did you actually use, and which items brought you the most comfort? What can you leave behind next time? What can you replace with lighter items?
My first really light backpacking trip was a true test in the mountains of Colorado. It rained or snowed every day. I went 110 miles without a blister, climbed 5 "fourteeners", stayed warm and dry, and never had more than 17 pounds on my back. Oh, and I never had as much fun with a heavy pack. That was lightweight backpacking at its best.
About the Author: Steve Gillman is a long-time backpacker, and advocate of lightweight backpacking. His advice and stories can be found at http://www.TheUltralightBackpackingSite.com