Looks like we jumped the gun on this one - turns out regular 10.1 nightlies aren't actually yet available for the GS, and the solitary build was triggered manually as a test. Sorry to get your hopes up, guys!
Up to this point, we've only seen official CM 10.1 nightlies show up for the Nexus 4 and Nexus 10, but an unlikely device just got its first taste of Android 4.2: the original Galaxy S (I9000). The builds are currently marked as "experimental," so if you're looking for something stable, this probably isn't the best direction to go.
Definition: A "nightly" is a bleeding edge release that is built on a daily basis, usually at night after a full day's worth of new code has been committed.