Must say that I don't know a single person who uses Vista, not one.
The problem is that Windows hasn't really gone anywhere in the past 8 years either. XP was really only Windows 2000 with a little polish and marketed for the home users. I'm not sure what Vista is, but it certainly doesn't appear to be an improvement over what was previously available. If you think about the tremendous strides Linux and OS X have made in the same timeframe Windows appears to have come grinding to a halt in comparison.
On the Linux front we have much improved hardware support, an array of very useable desktop environments to choose from and widespread adoption of advanced package managers just to name a few. The package managers alone are huge leap in usability. Installing software on Windows seems primitive in comparison.
On the Mac front, we've seen the move from OS 9 to OS X, five revisions to OS X with each being more polished than the one before, support for two CPU architectures, a transition to 64 bit without any headaches and too many major features to even name. What's really interesting is that many of Apple's new features - Time Machine and Spotlight to name a couple - aren't really new innovations. Apple has just been the first to deliver them to average users in an easy to use package. That's a space in the market that was traditionally occupied by Microsoft.
I wonder if what's happening here is that people are finally getting wise to the fact that Windows has basically been stagnating for the better part of a decade while the competition has been making steady and consistent progress.