
No problems whatsoever
Upgraded using package manager on 4 machines, from a 400Mhz Celeron with 128MB up to the 3.3GHz Core2 4GB with each having different chipsets (AMD, Intel, nvidia) , graphics (ATI/AMD, nvidia, intel, neomagic) and RAID (none, RAID0, RAID5) configurations. 2xXubuntu, 2xUbuntu and not a single problem on any of them unless you count the addition of a couple of packages and services that I didn't want.
That was not the case with 9.04 or any previous version so it gets a big thumbs up from me!