The main thing about linux (and as I've noticed this afternoon, osx) is that people don't bother with it. If there were more than just the zealots and hardcore nerds working with it and developing for it, there might be a reason for everyone else to use it. Right now, they're working on it, but it's slow, but then windows has been standing still for a long time, so if vista leaves a bad taste in enough people's mouths, they'll have even longer.

(also I wish I had enough time to fiddle with osx to make it Just Work. it's nearly as irritating as ubuntu sometimes!)