@Jeffro - LOL, the early bird catches the worm!

Yeah, it's another tricky question. The codex is quite separate, being on a subdomain, but the forums and extend seem a bit more integrated, being in subdirectories.

I'm guessing they're not rocking Drupal or anything, maybe Matt's kicking it old school with b2? My best guess would be that WordPress.org is primarily running on WordPress MU, with the other sections powered by other apps hanging off of that.