The 360 version of the new Dragonborn DLC will be released on 4 December but there was no date released for the PC a few days ago when it was announced. In a short tweet from Bethesda this evening they posted
“We’re also close on new Skyrim content for PS3 and PC”.
The PS3 content is lagging behind, much to the annoyance of PS3 owners, and both the 360 and PC have already received the Hearthfire and Dawnguard DLC . We therefore have to assume that this latest tweet refers to the new Dragonborn DLC so keep an eye out for a release date in the coming days.