I was playing around with Karmic on a IBM thinkpad with ATI Radeon Mobility 7500 M7 LW

a) I installed initially via the standard install routine - no via the live cd. Booted up - after about 3 minutes screen froze requiring a hard reboot. Rebooted - happened again - and then got a corrupt grub2.

Checked Xorg.log for errors - really didn't see any.

b) Installed again via the standard install routine - this time I uninstalled compiz - Again after a while I got screen freezes and corrupt boot record.
c) This time I tried the live cd. Wow - sweet - no problems!!
Little bit of screen corruption - so I disable compiz. Most of the corruption goes away.

So recap - most of the video performance issues from 9.04 have gone away. However - When I install not via the Live CD I got freezing even with compiz disabled and corrupt grub2/boot record.

Everything else seems to work perfectly (sound/wifi....etc)