Now we know why Apple didn't release an updated iOS 4.2 beta for iPhone, iPod touch, and iPad last week -- they just released the GM (Gold Master) for developers. This is the typically the final version given to developers ahead of time so they can test it on their apps and make sure everything is working before the release goes public.
No word yet on what if any changes or new features might have snuck into this iOS 4.2 build, but if you come across any let us know in comments or drop us a line.
Check out our complete iOS 4.2 beta walkthrough for the features so far.
UPDATE: AirPlay is still audio-only to Apple TV. Maybe iOS 4.2 for Apple TV will be required to enable that? There's a new AirPlay icon, however, and the multitasking dock has even more functionality than before. Pics after the break!