I recently logged in to my Steam-account because I wanted to check out it's status. Mostly since Valve announced they will be releasing the Steam-client for Linux. And to my surprise, all games I had bought earlier were still available in my "Library" :)
I had bought "Counter-Strike" (the original) a few years ago. Though it was the CD-ROM release copy, it included a booklet on activating the product on Steam.
I'm SO glad I actually did, because I can no longer find the original CD-ROM, nor can I find the DVD-ROM for Half-Life 2 / Counter-Strike: Source. But that didn't matter :) Steam had all the games, already activated and ready to download and install :P Woohoo!
If they are successfull at porting the client to Linux, and consequently; games. They will definitely have opened a whole new market-target for online game distribution ;)
Way to go Valve! ;D
Coincidentally, Valve recently published a press-release claiming Linux as the new de-facto open (gaming) platform. Beating both Windows and Mac OS X on the "technicalities" ;P
Linux, being an openly developed platform, gives game-developers a technical road-map of the OS' inner workings, it's limitations and structure details that give an immensely comprehensive base for advanced game programming.
Personally, I don't think they've even tapped the tip of what is possible with a Linux-system when it comes to serious gaming. I see promising development if this takes off, as we all hope it does :)
PC Games N:
http://www.pcgamesn.com/article/valve-linux-better-windows-8-gaming
Norwegian e-zine:
http://www.idg.no/computerworld/article259040.ece
http://www.idg.no/computerworld/article259040.ece