Currently I'm running a desktop on XP and a laptop on Vista.
I dont mind Vista at all, it is a little unintuitive compared with XP, but you get used to that. What don't I like about it? Well, not much, if I'm honest. I dont like the start menu; I much prefered the separate bar when you clicked all programs, and I would prefer an option of something like the XP start menu, rather than just Vista and Classic. The only other thing is the options for switching off and logging off, but I'm nitpicking now. The only other issue is the number of processes running, currently my laptop doesnt have that much on it, but it's running 73 processes, compared to the desktop which is full of crap and running loads of unnecessary programs, which usually sits in the low 60s.
Apart from these, I have no problems with Vista, and I got used to it pretty quickly.