The specific feature set included with the Steamworks will be cross-platform match-making and play, friends lists, chat, and achievements. It will also include Steam Cloud saves, allowing users to start a game on the PlayStation 3 and continue it on another PS3.
Similar to playing PC games on Steam, it will serve as an overlay within the game itself. This lets users quickly access Steam friends, game invites, and so on. Steam Achievements are also linked to the account, so you'll be earning them and PlayStation Trophies simultaneously when you play on PS3. Score.
You'll need to link your PlayStation Network account to your Steam account in-game to access the features, but it seems like a simple enough process. And of course, if you don't have an account, you can create one for free. Valve has set up a FAQs page for more information.
Portal 2 is due out for the PC, Mac, PlayStation 3, and Xbox 360 next Tuesday, April 19. If you've got a hankering for more Portaly goodness before then, check out our recent preview and interview with project lead Joshua Weier and writer Erik Wolpaw.