Valve has launched an official support page for those intending to make use of Portal 2's Steam features on PS3.
The lengthy Q&A goes into much more detail than the earlier announcement about how the Steam service will work when it debuts for the first time on a games console on PS3. It also handily includes the first glimpses of what the system will look like on the Sony console (images on this page).
There are no major surprises - it looks much like the PC program, with the dark grey interface and a top menu of options including Chat, Friends, Achievements and News.
Evidently, Steam will run in the background while you play just as it does on PC, and can be called up at any time by hitting the Select button. It looks like joining friends' games will be as easy as highlighting their name and hitting 'X'.
The Q&A through the link below details how exactly you'll be able to link your Steam and PSN accounts, how multiplayer games will work and how you redeem your free PC/MAC copy of Portal 2 that will come with the PS3 version.