As noted by Joystiq, trying to access your cloud saves is resulting in a 0x807b0198 error for many, although other parts of XBL like streaming video services and multiplayer gaming profiles are unaffected.
While the overall Ultraviolet sign-up process and its multiple logins hasn't gotten any easier, once we created a ParamountMovies.com account we were able to stream a copy of Hugo unlocked by the Blu-ray 3D version in HD just by signing into the free app (XBL gold subscription required) on the Xbox 360 -- no antiquated discs necessary.