For your folks who like to compile and run your own ROMs straight from the source (and who doesn't?), know that the Android 2.3 Gingerbread source code is being pushed to the Android Open Source Project right ... about ... now!
For 90 percent of us or so, this doesn't mean much. But for you developer types, it means you can download the base code straight from Google.
Interestingly enough, however, is a warning against using the AOSP code to roll a version for the Nexus S. Says Google's Jean-Baptiste Queru:
"Even though Nexus S is designed to be suitable for AOSP work, there
are some caveats. I very strongly recommend against trying to use
Nexus S for anything related to AOSP at the moment. Trying to unlock
or use your Nexus S for AOSP work could easily turn it into a Nexus B
(where B means "brick"); I have two of those, they're not very useful.
I'll send some guidelines about what is currently possible once I've
finished pushing the source code. "