It's been mentioned elsewhere that there seems to be a rule that a relatively decent iteration of a Microsoft OS will always follow a crappy one, and vice versa. Thus:

Windows 3.1: Decent enough to be industry standard for many years (not that it was great, there was just no alternative at the time)
Windows 95: A step up in the UI dept, but horribly unstable
Windows 98: Worked out a lot of the bugs (though not all)
Windows ME: Reintroduced a lot of those bugs
Windows XP: 10 years old now and still industry standard in many places
Windows Vista: Introduced a lot of unwanted security features, very bloated
Windows 7: A step up in almost every sense. We have it installed on 6 out of the 8 PCs in our house (the other 2 are Linux machines).
Windows 8: I don't know why anyone would think that I want my desktop to look like an iPhone, thank you very much

I'll be on the lookout for Windows 9, but until then I'm very happy with what I have installed now.

-- Ben