64-bit XP on the primary desktop, 32-bit XP on the primary laptop, Windows 2000 on the ancient tiny laptop. Linux on a second desktop.
I used to hate XP, but it grew on me after I got a job and had to use it every day. I figured out how to fix the things that annoyed me about it. I used to have a Vista laptop, even used it for a few months before I sold it to a friend to partially pay for a new laptop, which also had Vista (64 this time). I hated Vista though and replaced it with XP as soon as I got it.
I also tried Windows 7 on my laptop and desktop and wasn't impressed (no real benefit and much more annoying), and went back to XP. I intend to try Windows 8.
Basically XP is just what works for me.