I'm running latest retina macbook and apple TV, and yes they are on the same subnet.
This used to work...not sure why it has now stopped entirely, now. Cannot even share music from mac itunes on apple TV. Really at a loss at how to diagnose and fix. Both apple TV and my mac are able to connect to the internet, but they seem to not be able to see each other. I have allowed signed app's to receive incoming connections, even turning off mac firewall entirey doesn't help. Going into system prefs=> displays, Airplay mirroring - no devices detected.
MacBook Pro (Retina, Mid 2012), OS X Mountain Lion (10.8.2), apple TV