Borderlands 2 will allow you to take you couch co-op companion online. Gearbox's Steve Gibson told Joystiq at the Gamescom reveal of the game that those playing split-screen will be able to go online and connect with two other players.
"The only situation you can not do is split-screen plus split-screen because you need a host," Gibson said. "And a split-screen guy uses a lot of CPU, so he can not be the host."
Another improvement for the sequel concerns the user interface, which has been reworked for split-screen. Now you can easily manage the upgrades menu without all that awkward scrolling around.