Just last night I found a post on TUAW about something called AirParrot (http://www.airparrot.com), which provides similar functionality. I've been looking for something like that for a while, so jumped at the chance to download it (cost me $9.99). It's in beta, and the developer makes no secret of that. It does not pipe audio, and has a few other quirks but I managed to: run a powerpoint presentation, run civilization v, and play some youtube videos from my machine to my appletv. I have no affiliation with the developer, but i must say - to pwthornton's point above, it's pretty effing cool to airplay out of your mac. I bet the official release from apple will be that much better too.