In my experience, Windows doesn't need to be rebooted very often - although it does seem to leak some RAM. Also, a few games and other applications (like GTA:SA) cause lockups or BSODs in edge cases. GTA:SA freezes the computer if I pause it, close the laptop lid, reopen the lid, and try resuming.

Also, as you mention, drivers cause problems occasionally. I think twice Windows suddenly stopped recognizing a wireless mouse, not sure why. It worked on a different USB port.

Disclaimer: I'm talking about XP. Also, I have little experience in Ubuntu, but quite a bit in FreeBSD on the desktop. Once it's set up, it works quite nicely actually - apart from some quirky behavior while suspending to RAM.