I just bought an iMac back in August of 2012. It is a Mid 2011 model. We also have 3rd generation apple tv. I have no air play in display settings which according to apple means its not supported on my imac. Something is clearly not right here since my computer is a mid 2011 iMac which is stated to meet the requirments for airplay miorroring. I'm confused and frustrated.
iMac
Your iMac is up to date (10.8.2), correct?
Have you ensured that the Apple TV is up to date and both are on the same network?
So I just talked to someone at apple support and apparently I'm not running mountian lion (I have 10.7.5) which is the issue. My frustration here is that when I ordered the mac back at the end of August it said it included mountian lion. I never even checked to make sure. Since this is my first mac I had nothing to compare the OS to and didn't think anything till this came up. Now it's probably too late for me to request a free upgrade... ugh irritating.
Ah, that is frustrating. You can always see what you're running by clicking on the Apple (top left) and selecting About This Mac. Yes, I imagine it would be too late for the free upgrade (you can try). However, at $20 it's not too much of a hassle.
Mid 2011 iMac with no airplay in displays preference
