I really wish I could fit everything I needed in life in a single backpack. I try to follow that philosophy, but it's very hard to get rid of things. I agree with Miguel, it's harder to pare down possessions than it is to lighten pack weight.
Several years ago, I quit my job and backpacked in New Zealand and Australia. In preparation, I got rid of everything I owned except for my clothes, guitar, computer, and a few boxes of books and CDs. But when I got back from my trip, I started getting more stuff again.
I'm in the middle of trying to purge it, but there are always reasons to keep something. "I don't use this backpack, but my fiance might want to come on a trip with me so I have to keep it." "I don't use these plates, but I might need something nice for guests (nevermind that guests are happy to use my less fancy plates)." "I don't wear these clothes, but I might need them in case I loose my job and start working at a place with a dress code." Most are not good reasons, but unless you have a real incentive to get rid of stuff, you'll accept a silly reason.
I'm getting better at fighting the urge to keep things, I've got several boxes of clothing, kitchenwares, books, and CDs to get rid of, I just need to take the time to go to Goodwill and used book and CD shops. I'm still not getting rid of enough stuff, but it's a start.
I'll definitely check out unclutterer.com.