Well the same reason that I never last very long running linux on my laptop is the same reason why I’ve reformatted. Games. FFXI doesn’t work to happily on vista. While I can play it, after a while it locks up the machine, and thats just annoying.
One of these days game makers are going to start porting their games to other OS’s more often (like Linux) and when that starts happening the mass migration from Windows will begin. Lets face it, for alot of us, games are most important.