we now have gaming desktops for Linux and good support form Nvidia AMD Intel it's only a matter of time before Linux Gaming Desktop out numbers apple seeing how Mac OSX is Locked to Imac's macbook pros macbook airs Etc and given the development of Linux in the recent year i can say Linux Gaming is starting to look really good for developers Steam has 97 games for Linux and yes we have MMO's on Linux as well i love to see Blizzard Supporting Linux
Nvidia & Steam Porting games to Linux
The Activision and Raven Software game studios have open-sourced two of their games for "for people to learn from and play with" the code.
Alienware X51 Gaming Desktop with Ubuntu Linux
Steam OS is based on Linux
Build your own Steam Machine