I upgraded from a PIII-133Mhz FSB w/786 Mb RAM that has been a workhorse for 8 years.
I'll likely own a Mac someday. But for the foreseeable future, Winders and Linux do me just fine.
I said that for a couple of years... I just purchased my first Mac. Windows was always good enough for me, until... Vista. I made the mistake of purchasing a really nice system with Vista. It's really slow. The system is a dual 3.2 Ghz with 3 Ghz of RAM, TV tuner, upgraded graphics card and some other parts.
Before that, from newegg.com I built a 3.2 Ghz system with 4Gb of RAM and a Terabyte of disk space, a TV tuner, updated graphics for ~$1200... and I put XP on it. It was a nice system! But then I put Fedora Core 6 on it and it really flew!
I think Vista has a nice GUI look and seems fairly stable. It's just really slow considering the hardware.
I'm now switching our Windows systems out for Mac. The wife will get a 24 inch iMac, the kids a 20 inch iMac and I'll probably get the Mac Pro one of these days. For now the 17 inch Mac Book Pro I'm using is really nice... and it's real Unix underneath!