What do you GPL advocates want?! Linux is for everyone to play with and use. There's no definite timeline of when you should merge changes into mainline kernel. There's nothing that states everything surrounding linux has to be GPL either. I'm happy Valve is investing time on my fav kernel OS, whatever it may be for. It sure won't harm Linux much having another company looking at the Performance issues we currently have with OpenGL and drivers. Steam for Linux is just a less intrusive DRM, it's not SafeDisc or Securom. Some games will be DRM free. Some will use their own, you can avoid those.
I hate when you filth shun away from the word DRM without even acknowledging that Valve needs to use it to be successful in their business. They aren't the Humble Bundle or your Local Open Source Developer for Free company you know. Who said you ever must Install Steam in the first place to run Linux, it's not bundled with it is it?
Sheesh: I for one would love a reason to never boot Windows again, Source Engine is one of those. I've got Calligra-Suite for office work, Blender for 3D, and Renoise to make music in. And all my banking business works through Linux.
Just because some of you seem to hate games, I do not. In fact I've purchased more games ever since I started using this OS.