If you go to here, you can access and download the release candidate for SP1 of WSUS 3.0.
The biggest addition to SP1 is support for Windows 2008 and integration into the Server Manager as an available role. As usual, some known issues of 3.0 RTM have been addressed in SP1.
If you are using WSUS 3.0 and not experiencing any problems, wait for the official SP1 release. If you want to be bleeding edge, give it a try, especially if you want to run it on your Windows 2008 boxes.
Note: If you receive an error trying to access the Connect site, you may need to log in with your Live ID account, go to 'Available Connections' and join the WSUS 3.0 SP1 program before you can download the bits.