Apple has just released iTunes 10.6.3, which helps set up developers to upgrade to the new iOS 6 beta, which arrives today after this morning's keynote. Even if you're not a developer, you can get the update to the app on the official iTunes page, and though we don't see it in Software Update just yet, it'll presumably be there soon as well.
Other than the beta download, there's not much else to this one. Developers can grab the beta today (though be warned that it may not be stable quite yet, and you may have to restore your phone when the official version is released). As for the non-dev public, iOS 6 is due out sometime later on this fall.