This is cool. Support for PSN has appeared in the latest Steam update. If you logout, next time you login you’ll see a dialog like the one above with an option for “Playstation Network Players”. If you click the “FIRST TIME SIGNING IN” button you’re brought to a page asking you if you have played the PS3 version of Portal 2, and if you have you can login using your PSN credentials.
If you have already played Portal 2 on PlayStation®3, you can sign in using your PlayStation®Network login.
Once you have signed in, you’ll find your profile on the Steam community includes information about what you have been doing in Portal 2. You’ll also be able to play your copy of Portal 2 on your computer by redeeming the code provided in your PS3® Portal 2 box.