Though rumors (and some slick yet ultimately fake video evidence) to the opposite effect has been circling 'round the internet for some time now, Rocksteady game director Sefton Hill confirms in a recent IGN interview that Batman: Arkham City will be "a 'single-player only' experience." According to Hill, the developer didn't want to lose resources that could have been spent on perfecting the solo campaign. "With the game now coming to the final stages, I can honestly say it would not have been possible to deliver Arkham City the way we wanted to if we'd have added multiplayer."
Well, shoot. We were really holding out hope for a Batman and Robin co-operative mode, in which one player does all the crimefighting while the other comments on things that are holy -- until being bound and captured by lower-echelon thugs. Oh, well!
For more info on things that are actually in the game (including classic supervillain Hugo Strange), check out Rocksteady's discussion with IGN.