If you were counting down the days until you got to return to the Bioshock universe, you're going to have to adjust your calendar: the newest game in the series, Bioshock Infinite has been pushed back to 2013.
February 26, 2013, to be precise, according to the recent message from Bioshock creator Ken Levine. In a message on the game's website, he said that he and his studio were "doing things that no one has ever done in a first-person shooter", and that in order to implement "some specific tweaks and improvements (that) will make Infinite into something even more extraordinary", the game's release date needed to be pushed back four months.
Additionally, the game won't be getting showcased at any of the usual gaming events; in Levine's words, they're skipping E3 and GamesCom to that "the next time you see our game, it will be essentially the product we intend to put in the box".
While the delay is certainly unfortunate, it didn't take some people to connect the dots and come up with an explanation for it: as both NeoGAF and Kotaku note, Bioshock publisher Irrational currently has a job opening for someone to help with "the networking aspects of BioShock Infinite". There are obviously multiple ways that networking could be integrated into the game, but it doesn't seem like too much of a stretch to believe the game might have some multiplayer component to it.