XP was tolerable. Performance wasn't too bad. Being a vector for viruses wasn't fun, but if you watched yourself you could usually get your work done. When my elderly laptop died I bought a nice refurbished HP desktop that came with Vista. There are no shortages of rants on Vista, so I'll be brief. It seemed to be a RAM hog and applications froze and died on it just too much - even Internet Explorer. Man, at least the software made by the same company that made the operating system should work.
While I need Windows for certain purposes (testing, for instance), I knew I didn't need it for everything. I'd long been a fan of OpenBSD, but didn't want to spend huge amounts of time setting up my system - especially if I ended up doing it more than once every 6 months. I wanted something closer to OpenBSD than Windows, but something that I could use nearly right away. I like heavy, consistent improvements and a community over perfection, so with all the attention give Ubuntu I thought it deserved a try.
A few months later, it's my primary system. I'm booting into Windows less and less often. I've had to figure stuff out. It's not perfect, and I'm nearly certain that since I'm on a dual processor dual core AMD64 system makes it a little trickier. I'm sure with time it'll get better. In the mean time it's nice to have more visibility into why things don't work - so when Firefox dies I can start it up from the command line and see what caused the croaking.