Ubuntu is bomb.
I'm a huge proponent of open source apps, but my absolute hatred of pretentious Linux followers prevented me from biting the bullet and installing a build of it on any of my machines.
I finally broke down last year and started with Fedora, then changed over to Ubuntu this year. I'm dual booting Vista/Ubuntu on my laptop, and I'm running Fedora 9 through Virtualbox on my desktop.
At this point Windows has been ingrained into my skull, so I'll always prefer it for personal use, but I admire the hell out of Linux. Plus I could spend hours tinkering with the damn thing.