Though Steamworks isn't being allowed anywhere near the 360, for the time being, PC and PS3 owners will at least get to play together - or fight with each other in Portal 2.
Valve have been beavering away trying to finalise netcode to enable steamworks to effectively cross pollinate online game play between console and PC. It's not a new idea, but it's never quite worked as smoothly as it could in past endeavours.
Exciting stuff. Wonder if the PS3 version will have mouse and keyboard support though...