While PSN owners got their Scott Pilgrim vs. the World DLC, the one that includes that patch to add drop-in / drop-out co-op, about a two months ago, Xbox Live Arcade gamers were left waiting in the wings. The content pack also adds in a new playable character, a dodgeball mode, and a new arena all for the price for $2.
Both the patch and DLC are finally out on Microsoft's console, though it wasn't without some hiccups, as the content originally didn't work at all according to Joystiq. As of yesterday though, a forum post on the Xbox Forums from an Xbox Support staffer has confirmed all should be well in the world of Pilgrim. You may commence your dropping ins and outs - but only if you do it locally.