I have had the same issue since my last update.
I have done the following:
1) reinstalled itunes after removing itunes and bonjour
2) hard connected my appletv to my router via cat 6
3) set my router to only wireless G
4) manually set my IP address on my router to ...102 and on my apple tv to ...102
5) restarted router and apple tv2
I get homesharing for 5 minutes then lose it. Oddly sometimes my ipad library can be seen by ATV2. My itunes thinks homesharing is on.
If I turn Homeshare on and off it works for another 5 minutes from my PC.
if i reboott Itunes it works for another 5 minutes.
I wonder if this is a clever way for apple to get you to subscribe to itunes match
Any other suggestions than those above? I think it's clearly Itunes - ATV works fine every other way - I can watch my purchased programs and music from the cloud via match for music and movies/TV if I have bought.