Our esteemed colleagues at Joystiq spoke with the excellent online rental service GameFly about their plans to carry Manhunt 2, or, more to their point, their plans not to. According to a GameFly rep, "GameFly as a general policy does not carry AO rated titles." That makes sense, since they only serve customers 18 and up and deliver games directly to said customers' homes. And to be clear, by "makes sense" we mean "doesn't make any sense at all."
Blockbuster isn't going to carry it either, but that's less of a surprise. Blockbuster has a long-standing policy of not carrying NC-17 or equivalent movies.