I'm surprised you picked XP as the falling point. I didn't enjoy the days of reinstalling 95/98/ME every 6 months to avoid driver weirdness and seemingly random failures. XP was built on the foundation of 2000, which tended to make it more robust vs. its predecessors.
Vista on the other hand...
I mean, part of it is that I really hated the Fisher Price look to it, but it was also the first time I ever felt like I had to "hack" things to make stuff work. I had to muck with registry keys. Oh, and it was the first time that I noticed that Windows repair tools do not work.
I suspect I might have hated 9x more but I was pretty young when they came out and I didn't really "get into" computers until XP, and I disliked it enough to dual-boot Linux as a twelve year old.