We've known for some time that Valve's hotly anticipated first person puzzler Portal 2 would be the first foothold for bringing their Steam service to the PlayStation 3. But today, the much-loved studio has sent along a new press release, detailing the full extent to which they'll be rocking the platform come April 21st.

Key highlights include:

• cross-platform gameplay, matchmaking, friends, chat, and achievements
  
• Steam Cloud saved game support for both co-op and singleplayer games (but PS3 saves aren't compatible with PC/Mac).
  
• Steam overlay gives access to both PSN and Steam friends lists and navigation or text chats, player profiles, friend requests and game invites.
  
• Steam Achievements are earned in lockstep with PSN Trophies and are also accessible within the Steam overlay.
  
• This functionality is activated by linking your PSN account with your Steam account through an in-game interface.
  
• Linking a PS3 version to your Steam account permits you to access and play the game from a PC or Mac and is done by redeeming an in-box code on your computer which will then list Portal 2 among your PC/Mac Steam games.

So basically, if you're buying a boxed copy of the game and you own both a PS3 and a PC/Mac, it's a no-brainer to pick up the PS3 version.

That said, Valve don't practise regional price variations with their own online-purchased products. So if you only want it for PC/Mac and don't care for a box, you'll no doubt be able to pick up the game significantly cheaper directly from Steam.

Xbox 360 users unfortunately only have the brick-and-motor option for now, as Microsoft remain unaccommodating for Steam functionality on their platform.

Dependent on no further Valve-time anomalies, Portal 2 is due to launch on PC, Mac, PlayStation 3 and Xbox 360 on April 21st 2011.