Hi All-
I have been having similar problems on my AppleTV2 for the last few weeks. I read all of the suggestions here, but was having a lot of trouble tracking down the specific cause since the iOS was updated, iTunes was updated and Mac OSX had an update all around the same time.
My symptoms:
We use the AppleTV mostly to stream TV and Movies from my iMac iTunes library to the AppleTV. My problems started after returning from a vacation at the end of March. I know the iOS update came out during the last 10 days of March. Once back, the AppleTV kept dropping the connection to the iTunes library at random intervals, it might be an hour it might be less than a minute. Once the connection was dropped, the AppleTV would drop into the main Menu and would list my shared library under the Computers heading, but would not show recent items above the menu (pictures from videos or album art). When I would click on the shared library 1/2 the time it would say it was not connected, then quickly start loading the library (but that may just sit there and spin, so I'd hit menu and then it may or may not have made a solid connection to the library). When I finally navigated back to the program I was watching it might work for a minute, up to 10 before dropping again. I found no difference in behavior between ethernet and wifi. While this was not working the Netflix streaming service worked very well.
Solution:
I finally tracked my issue down to Intego VirusBarrierX6. I had been using VirusBarrier for several years, and have had issues in the past, but the newest version introduced an automated updater, so I didn't realize it had run a recent update. With version 6 they integrated the firewall (Barrier) into the Virus scanner (it used to be a separate app I think) and even though I had "No Restrictions" set in network traffic and had added my local network to the trusted sites I think their firewall is the problem. I noticed a new check box in this window I hadn't seen before that said something like allow AppleTV, so I tried checking this, no fix. So next step was I uninstalled the software and now I have had 24 hours of problem free AppleTV.
I hope this helps anyone else who is having similar issues.