Xbox.com also faced similar problems yesterday; not being able to display user profiles and being extremely slow were a few of the problems. Microsoft stated that they were aware of the problem, and were actively working to correct the issues.
While I have been unable to try it yet, Xbox Live's Major Nelson has posted on his Twitter that "the storm has passed..." Live always seems to have an issue after system maintenance, it seems. Hopefully all of these bugs are worked out and Microsoft is well-prepared for the strain of the New Xbox Experience update coming later this year...