I don't think anyone is surprised by the news, given the success of Paranormal Activity 2, but now we have official word along with a release date thanks to Bloody Disgusting. Paranormal Activity 3 is officially scheduled for October 21, 2011.
There is no word if Paranormal Activity 2 director Tod Williams will return for the third movie, but given the fact that he is in the middle of pre-production on another film, it seems unlikely. With the film's release less than a year away, more information on the director, storyline, and cast should be released soon.