Those of you (us included) who were intending to go mouse/keyboard style with the PS3 version of Portal 2 are out of luck. It won't be supported, Valve has confirmed.
When asked about PS3 mouse/keyboard support, Portal 2's project lead Joshua Weier told the PS Blog: "No, unfortunately we don't do that. The whole game is built around playtesting, which extends to the hardware and how people use it."
He went on to explain: "We have people internally who played on the PS3 - we use it all the time - and we constantly iterated it."