Oh shit, yeah this thing is out now and Steamplay enabled! I had purchased the game during a Steam sale back when I had a PC, and low and behold: The Witcher: Enhanced Edition is now showing up in my iMac's Steam library under Mac Games.
Fuck yeah!
EDIT: So let's pretend that I've never really gamed on my Mac before, but I do have a 360 wireless adapter left over from my PC days. Is there an easy way to get that thing working on the Mac, and in games like The Witcher? I don't mind spending a few bucks on the Mac App Store if that's the easiest way. I have PS3 controllers too, but I'd prefer 360 if there's a way to make that work. Anyone know?