Apple has just issued a third beta build of iOS 6 to developers. The new software has not yet appeared on Apple’s iOS Developer Center though devices running iOS 6 Beta 2 can update over-the-air (go to Settings > General > Software Update). The update prompt mentions only "bug fixes and improvements" so we're doing some digging as we speak and will update when we find out more...
Apple seeds iOS 6 Beta 3 to registered developers