Alienware, the Dell owned gaming computer manufacturer, is now offering Alienware X51's (My Machine) pre-installed with Ubuntu Linux rather than Windows 7 or 8. In my opinion I an quite excited, I love Linux, but the only area that it is not up to snuff with is high end gaming. Ever since Stream was announced for Linux, the opportunities for gaming on the OS has gone into overdrive, and looks like even Alienware is attempting to see what they can do with it. It looks like these computers will also come with Steam per-installed as well. Since Ubuntu Linux is free, the computer is even $100 less at $599 vs $699 for the Windows equivalent.
As or the machine itself, I own the Windows 7 X51, and I'm quite pleased with it. It is a very compact, yet powerful machine, that I can connect to my own monitor or the HDTV in the living room. I run Linux Mint on mine through Virtualbox, and have a Windows 3.11 setup through DosBox.
To read more info about these machines go here. To learn more about Ubuntu go here.