I game on my iMac. Currently just played through BioShock Infinite, and play StarCraft 2 daily, and really should get back to Guild Wars 2 at some point... but yeah, I'm considered odd by my friends for doing so.
Throw in Diablo 3 and Portal 2 into the mix and you've got what I'm playing these times around on my rMBP13's HD4000. I've actually run through both SC2:LW and D3 on a '09 MBP. Sure you don't get all the bells and whistles, but a steady 25fps (capped through INI settings) matters more to me than shiny effects and had the games be perfectly enjoyable.