Actually, when XP was released, the next version of windows was scheduled for 2004/2005.
It's just that much longer for FireFox to gain market share, because (for the most part) people aren't going to get IE7 until the next version of Windows comes out.
And it gives Mac and some of the more user friendly versions of *Nix a chance to get a bit more of a foothold.
2 years ago, I was running 3 Windows machines and a Mac. Now it's 1 Windows, 2 *nix, and a Mac.
In the past year, I've converted a half dozen "Joe Average" users to *Nix. Not one of them ever wants to go back to Windows. And now I get calls from their friends who want to give *Nix a try as well. (Most of which I advise to stay with Windows - I'm very careful about asking a person how they use their machine before switiching them over to Linux.)
I've also seen some pretty die-hard MSofties move over to Mac, because they want a more up-to-date Operating System.
Every month Microsoft delays, every one of their competitors gets stronger.
Will I get Vista? Probably. There are things that a Windows machine is simply better suited for than the other OSes. But I will most likely never go back to having more than one Windows Machine in the house. I've become too dependant on Linux.
I wonder how many other people could say the same thing? I wish I had some good numbers (not the fuzzy statistics that you usually see bandied about).