I'm certainly not a "gamer" any longer, but I still have a pretty healthy Steam library.
I've been very happy with the increasing options on Mac OS X and I hope they keep improving.
I'm way more excited about slower, turn-based games, and Civ V, Europa Universalis, and FTL have been enough to keep me from searching for anything else.
Despite this, I know I've been missing out on games I would probably love. I think I see a SteamOS device in my future.