Karmic just plain bites alot of users who were spoiled by Intrepid and Jaunty. They actually put some beta software in the final release! Inexcusable in my opinion for a "beginner-friendly" distro to put experimental, unstable software in a new release (PulseAudio, Grub2, etc). Jaunty is still supported. Intrepid is still supported. Even hardy is still good 'til April. Alot of users have gone back to older versions after Karmic borked their system.
But some good news:
Xubuntu Karmic does not ship with that experimental beta stuff. No PulseAudio, no Mono (if that matters to you). It has been far less troublesome than its big sisters. Just like families, lol, the littlest one is the sweetest!
More good news:
The next release of the 'buntu family is being built on Debian Testing instead of the usual Debian Unstable. Hopefully it will not include beta software. In the meantime, a previous release of Ubuntu is the best workaround.