I'm on 2.3.5, and ran across blogs where 2.3.6 was made available OTA by ATT in late November. I've been checking for updates regularly, but always get the message that I'm on the latest.
Anyway, called ATT yesterday, and they contacted Samsung, who told ATT that 2.3.6 was pulled back. No explanation was given. Sounds like it was a very minor update anyway, although ATT saw fit to release it (which is rare).
Guess this doesn't matter anyway - hope to see ICS soon