Jesus christ, just get a MDP -> HDMI adapter for $40 and deal with it.
AirPlay Mirroring isn't even that great. It doesn't handle surround sound at all and the system isn't upgradable in the least (in other words, expect Apple and Intel to come out with something even better in a year that requires even newer hardware) being that it is a HARDWARE FEATURE.
Seriously, if you're serious about watching stuff on the big screen with any reasonable amount of quality to it- just get an adapter and use that instead. The quality you get off a high-quality MKV source when using an HDMI adapter is infinitely better then that of what you get with Airplay Mirroring, partially because HDMI supports DTS-HD Master Audio and Dolby TrueHD whereas Airplay Mirroring does not. Airplay Mirroring also adds yet another stage of lossy compression to an already lossy-compressed video (unless you're playing a bluray disk).
I still don't know what the big deal is. People are acting like there's projectors and stuff out there that support this technology (when in fact there are none- nothing except the Apple TV works with it). It's an Apple gimmick, and it will be swept under the rug as soon as Apple figures out something better.
If your machine has a Thunderbolt or Mini Displayport on it, just use that and be happy. Buying a new machine is NOT WORTH IT for Airplay Mirroring, unless you're one of those people who goes crazy because they don't have all the most available up-to-date snazzy features.
-SC