I have ubuntu on my laptop and so far it's average. Flash videos (ie, youtube...) is slower than under Vista, trying to go full screen with video in any player causes the player to exit (changing from the Compiz WM to Metacity seems to fix that). Second time I booted it up it said something about the disk journal being corrupt and landed me at a prompt. Third time the same thing happened. Forth time (I was planning on reinstalling windows at this point) I was too slow to press F12 to select the windows DVD and it randomly worked.
This vid sums it up, really...