The game will launch in January, 2011.
How EA are going to bridge the gap between the first Mass Effect game (which was published by Microsoft) and its sequel is unknown, but we're assuming some kind of movie will be included on the blu-ray to fill players in on the events.
Update @ 16:52 — according to the game's press release: "The PlayStation 3 edition will include the full Mass Effect 2 game and hours of bonus content." No idea what the extras will be. Perhaps they'll be announced at the Sony press conference?