Gabe Newell described the PS3 version as "the best available on consoles" and it's slowly starting to sound like that's truly going to be the case.
Valves Eric Johnson has declared that cross-platform compatibility is strongly being considered for the PC, MAC and, yes, PlayStation 3 versions of Portal 2. According to Eric, cross-platform co-op is something the team are "gunning for".
And this was backed up by Valve developer Mike Dunkle, who confirmed: The plan is you will be able to play between console and PC.
It's the inclusion of SteamWorks on the PS3 version of the game that makes this possible. The XBOX 360 is tied up due to XBOX Live, whereas the PlayStation Network is more open to this kind of functionality. Hopefully this means we'll get plenty more Valve and SteamWorks support in the future.