GPMC SP1 fixes bugs found in GPMC sample scripts, GPO reporting, and in the Migration Table Editor (MTE). Interestingly, Microsoft have also addressed bugs found from Dr. Watson crash data. There's also a fix to the GPMC RSoP wizard to work when Internet Connection Firewall (ICF) is enabled on the computer running GPMC.
GPMC rocks! Oh - and here's something a lot of people seem not to know: you can use GPMC to manage a Windows 2000 AD. You can't run GPMC on a Win2k box, instead, run it on a WIndows XP box attached to the domain.