From Ars Technica:

Microsoft is taking down the Zune and Xbox Live services tomorrow to work on features that will be coming later this year.


Tomorrow at 12:01 AM PST, Microsoft will be taking down the whole Zune service, which includes the Zune Social, the forums on Zune.net, and the Zune Marketplace. At the same time, Xbox Live will also be offline, meaning the My Xbox section of Xbox.com will be unavailable, and the Xbox forums will be in read only-mode. Microsoft says that the downtime is scheduled maintenance and that it should not last longer than 24 hours.
Thank god they are starting to integrate!