Valve: Buy Portal 2 on PS3, get it on Steam, linked IDs, crossplatform play

[Xenostar]

Im assuming you will get it free and you could trade in your ps3 version, but like steam boxed games i reckon there will be a code in the box and once youve used it no one else will be able to link that copy to there steam account, so its second hand value will be greatly reduced.