Actually, I have to profess my ignorance in that while I've heard of Vista, I don't know what the hell it is.
Windows latest operating system. Some people don't like it because it is incompatible with certain hardware and it has a lot of "idiot-proofing" with regards to system operations.
However, I've had zero problems with it on my laptop, it's faster than XP on my comparable desktop, and I like some of the idiot-proofing from the standpoint of someone who always gets called when a friend accidentally breaks their PC.
I'm sure, though, Geoff can voice his own complaints. I certainly understand why people dislike the incompatibility, which is pretty stupid on MS's part.