Our good friends at xda-developers haven't kept us waiting long. Root access on the Nexus S has been achieved on the phone's day of release, and full instructions for replicating it are available at the link below. The Nexus S is the proud and so far only carrier of Google's latest and greatest Android software, so you're basically getting unrestricted access to the very best Mountain View can offer. Hit that source link. Do it.
[Thanks, Brad]