I think I may have fixed my Homesharing problem. I have a wall mounted plasma tv and my Apple tv was mounted on the wall right behind it. After trying almost very suggested solution on this site and the Apple forums, I thought that maybe something was interfering with the wifi signal. I read in the apple tv owners manual that nothing should be placed on top of the apple tv as it might interfere with the wifi signal. The top of my apple tv was velcroed to the wall and faced the back of my tv. Suspecting that the back of my tv was interfering with my apple tv receiving a consistent wifi signal, I decided to velcroe my apple tv to the back of my tv, but with the top facing outwards away from the tv. To my amazement, homesharing now works without cutting out. I watched a whole movie without it cutting out to the home screen.
I'm still not 100% sure that this solved the problem as I never had any problems with iTunes, YouTube or Netflix movies before. I'll do more testing this week, but I've never been able to stream a whole movie without it cutting out.
I just thought I'd share my experience with you all. Check to see if anything might be interfering with your apple tv receiving a consistent wifi signal. This might be a problem for some people.