John Resig says Google Groups is dead:
There is one area in which Google Groups continues to shine: Private, or restricted, mailing list discussions. However any attempts at using it for a public discussion medium are completely futile.
The primary problem with Google Groups boils down to a systemic failure to contain and manage spam. Only a bottom-up overhaul of the Google Groups system would be able to fix the problems that every Google Group faces.
Sad considering how well Gmail does at keeping spam under control.