definately all valve games.
im sure valve would let other developers make similar features using the steam platform but i dont think any of them will be bothered. maybe the ones who still support mods, may add it so ps3 users can play mods created on the PC versions but i highly doubt it because it would be easier to just port pc controls and tell people to connect usb keyboards/mice to their ps3.
i think their just making a big fuss of it because they want to prove a point to microsoft about opening up XBL.







