Update 4 [10:20 PDT on 3/31 - CF]: Everything should be back to normal, going by the Xbox.com support page.
Update 3 [18:30 PDT - GL]: The support page on Xbox.com shows a list of lingering issues on the Live service including account management, signing into Games for Windows Live on PC, and a number of payment and billing specific issues. On the plus side, the Xbox Live Operations Blog does report that the original issue with the release of the DLC before the title update was resolved at 11:00.
Update 2: "If you're getting 'communication failure' or 'unable to join session' errors wait a few minutes - we'll have them stomped out shortly," adds... Read More