I just read this on CAG i will just copy and paste what the person said:
"This is on both Kotaku and Joystiq: Valve announces that the PS3 version of Portal 2 will feature "full cross-platform compatibility: PS3 users can chat with Steam users, play multiplayer with them and even partake in cloud-based storage. The disparity between the PS3 and PC/Mac versions appears to be about non-existent now."
"If you play Portal 2 on PS3, you can play with people on a PC. Neat! And to make sure as many people as possible are doing just that, the PS3 version of the game will include the PC version.
"All players have to do once they get the game is link their PlayStation Network and Steam accounts. Once that's done, they'll have a Steam Play (so, PC and/or Mac) version of the game ready to download in their library list."
At least I now know which version to buy
