I've taken a couple stabs at minimalism (of possessions) in my life, staring when I moved from Austin to Seattle in 1995. I'm doing so again after relocating from Seattle to San Francisco a year ago.
There is absolutely no doubt that I've been happiest during those periods when I've had the fewest 'things'. I look back at the time when I downsized from a 1000 sq. ft. apartment in Seattle to 500 sq. ft. studio as the most productive and enjoyable time of my life.
Since moving here to SF, my wife and I have almost halved the space we occupy from a 1600 sq ft townhouse in Seattle to a very comfortable 850 sq ft. in San Francisco. I continue to get rid of the stuff and replace it with either 'virtual stuff' (e.g. electronic books) or just happily do without (e.g. espresso machine).
The main reason I 'upsized' from the small apartment to the large townhouse was that I felt like at my age at the time (30) I was 'supposed to'. I was the only one of my friends/work-mates that hadn't gotten married and/or had children, and bought a house. Oh, what a mistake! Now, ten years later, I'm so glad I'm back to shrinking the possessions in favor of a leaner, simpler life. For the first time since I was 16 I do not own a car. I have no debt (and with the exception of the townhouse and a couple years of credit card debt, I haven't since 1998).
I'm totally sold on continuing down this path, as she is as well. We don't plan on having children. We are both 40+ and enjoy the idea of moving around some more, perhaps even relocating overseas in time.