I read an excellent article by Paul Graham a while ago about the perils of accumulating possessions, and the way that they can weigh you down as you subconsciously worry about them. It's not a novel observation, of course, but he sets out the problem very clearly.
I also worry about how much 'stuff' I have, even though I'm not (by current standards) a particularly materialistic or acquisitive person. Even so, it's horribly easy to acquire a mountain of possessions, which becomes startlingly (and expensively) apparent when you move house. I hate buying clothes, but because of that, I don't throw away old clothes until they are literally falling apart. So even a very modest rate of acquisition of new clothes means that the storage starts to burst at the seams. You can imagine how bad the situation is for things that I enjoy buying, like music, books and electronics.
I've been trying to wean myself off the accumulation habit. My motivation is partly to do with reducing my spending, partly out of a wish to reduce my environmental impact, but also just to step off the consumer treadmill and have less stuff. Now that we have a library so conveniently close to our house, I don't buy books unless it's a reference book that will be useful for many years, or a particularly treasured novel that I'll read again many times. We rent DVDs from LOVEFiLM for general viewing, and only buy DVDs when we know it's something we'll watch many times (like The Big Lebowski or Firefly). I've also instituted a kind of self-imposed 'cooling-off period' for other non-essential purposes. If what I'm thinking of buying isn't replacing something broken, I make myself wait a month before buying it. I think about it, price up alternatives and so on, but I just don't buy it for a month. If I still want it at the end of that time, I go ahead, but often I find that the urge has worn off as I find that my life has miraculously gone along unhindered, despite the lack of that thing I thought was so important to my happiness. Don't get me wrong -- I like a lot of my stuff, and I'm not about to sit cross-legged in an empty white cube any time soon. I just want to whittle things down a set of items that actually enhance my life.
I also read a piece by Stuart Jeffries in the Guardian about the rise in popularity of services which allow rental of goods, rather than ownership. His point was that this was symptomatic of 'commitment phobia', but I actually think that renting rather than owning things is good thing (with the exception of the pet rental service mentioned - that's an appalling idea). It's an anti-materialistic feeling, and it's probably better for the environment: why own a car or bike or expensive clothes that you'll only use occasionally, when you can rent it and share the usage of one item with others?
I always laugh when I property shows on TV, where couples without children want a four or five bedroom house. Really, what are they going to do with all that space? Why do they need it? If they both work at home, they might need a couple of extra rooms to turn into offices, but after that, it's hard to see why all that space is necessary. The problem is a circular one -- as Paul Graham mentioned, the more stuff you have, the more space you need to house it all. But when you get a bigger place, you need more stuff to kit out the rooms as well (TVs, audio equipment, decorative items). Before you know it, you need a six bedroom house, even though there are only two of you. It's craziness, and I want to get out of it.