We have iTunes 11 on a MacBook Air with Lion (10.7.5, all current updates). Occasionally, in the middle of a song playing over Airplay, iTunes stops streaming the song. As best we can tell it appears to be random. If we go back to a song that it previously stopped on, but it doesn't stop again. Thought it may be Energy Savings settings, but it's set for 3 hours before sleeping, and 2 hours to turn off screen. Now "Put the had disk to sleep..." is set, and perhaps this is it. But according to my wife, this never happened under iTunes 10.x, it has just started with iTunes 11.
I'll try the "hard disk sleep" setting and report back, but any other ideas?
the new airport software and firmware fixed everything for me. Started by udating to Airport Utility 6.2 it then found firmware updates for my express and base station. Nice!