Some people are reporting that Airplay mirroring doesn't work on their Mac running Mountain Lion. Which Macs support AirPlay?
I Read an article today on cultofmac.com that start like this:
Unless you have a Mac from 2011 or later, don’t expect to be able to do this in Mountain Lion.
The reason, that people are according on, it's about DRM, because only Macs from 2011 and later have intel chips that are able to stream DRM content.
My best guess is that these Macs ship with Intel chips containing the latest and greatest version of Intel Insider, which allows streamed DRM encrypted Hollywood content to play — just guessing…