OK, so we released the news that SP1 is available for download a few hours sooner than I thought we would. You can download it now.
The release notes are probably the first place you should start to find out what is in it:
The ability to rename Domains is now supported with Exchange 2003.
Those of you looking for the exprofre.exe tool will need to download the Exchange Profile Update Tool at the following link:
Gotta attend the first session of Tuesday here at Tech-Ed, where we are announcing the release of Exchange 2003 SP1 (again), so I'll post some more information later.