I think it's going to be interesting to see if it takes off. Most STEAM users are windows gamers, and i doubt any of them are going to want to install Linux anytime soon, would certainly take some motivating them from Valve.
Halflife 3 exclusive to Linux.
tbh i could see that happening. I know Gabe isn't happy with Microsoft's closed app-store on Windows 8 and refuses to put Steam on it. Could see him trying to use Valve games to convert people to Linux.