I had a lot of problems getting Apple_TV_3 + itunes to work 100% reliably. Eventually I built a totally new server, used static ip's and I DID get a stable system that ALWAYS worked as expected re itunes home sharing -> Apple_TV.
Home sharing to iphone/ipad was hopeless (via music/video apps), the circle spinner would go for 10+ mins without listing the media. I therefore ran TVersity on the server and using the AirPlayer app on iDevices can play media fine so no longer use the build in apps, unless for media local to the device.
Since updating to 5.2 all appeared to be working well, however if Apple_TV has not been used for a few hours and I run the remote app, I CAN initially use the control part of the app, BUT pressing computer says "turn on home sharing blah blah blah..." If I then hit the button to list the devices, the updated ATV device is NO longer shown. However my OTHER Apple_tv (still on 5.1) IS still there, even though it has been sleeping for days. Both were 100% reliable before this.
I've done a Reset on the updated Apple_TV and set it to sleep after 15 mins and will monitor progress. I've downloaded the 5.1 ipsw, I hope Apple are STILL signing it. I'll test for another day or two but it it happens again I'll downgrade. If YOU have a stable system I would advise NOT upgrading to 5.2.
Does someone know what ports to block on router to stop the ATV checking and therefore relentlessly prompting you to upgrade, that's the only reason I upgraded to stop the messages.
Lastly since buying into apple-technology 2.5 years ago for the sole reason of anticipated reliability as though I have the ability I do not have the time to endlessly jump through hoops to make devices work as intended I have become very disillusioned. Unfortunately Apple seem to be just as hopeless as everyone else, re reliability, do they test anything?