Recent changes to Google Groups have caused the Groups link in the black navigation bar to stop working for the UMICH domain.
To get to your Groups, use this link: https://groups.google.com/. The Groups App is in the commercial domain, not in the UMICH domain, and is not covered in U-M's contract with Google.
We have opened a case with Google regarding the broken link. More information as it becomes available.
NOTE: This issue appears to now be resolved. Updated 8-20-13