***** SPOILER ALERT *****

Kotaku has found some infro from GateStop regarding portal:

Coming this holiday. Portal 2 is the sequel to 2007's Game of the Year and draws from the award-winning formula of innovative game play, story, and music that earned the original over 70 industry accolades. Features single and multiplayer co-op modes. The single-player portion of Portal 2 introduces a cast of dynamic new characters, a host of fresh puzzle elements, and a much larger set of devious test chambers. Players will explore never-before-seen areas of the Aperture Science Labs and be reunited with GLaDOS, the occasionally murderous computer companion who guided them through the original game. The game's two-player cooperative mode features its own entirely separate campaign with a unique story, test chambers, and two new player characters. This new mode forces players to reconsider everything they thought they knew about portals. Success will require them to not just act cooperatively, but to think cooperatively.

This more than confirms our belief that Portal 2 will have coop.

Kotaku has also found more information on Portal 2's Bad guy.

Cave Johnson, the boss of Aperture who was dead in Portal, will be the principle antagonist of this sequel. How? We'll get to that.

In the game, Johnson, described as an amiable self-made billionaire who refuses to accept the responsibility of his power, starts off as a sort of sidekick to the player but then he starts to lose his grip on humanity as the story progresses. According to an open casting call we received in 2008, at some point in the game, after Johnson has isolated himself from the people around him and lost touch with reality, he becomes the main bad guy.