From the SETI@Home website:

As of October 18th, 2010
"The machine that serves the BOINC database crashed. The projects are down until the recovery is complete. The current database machine has become too unreliable to continue as the primary DB server. We are going to move this functionality to the machine that is currently acting as the replica server. This will be a temporary fix, as this move will leave us with reduced throughput capacity. We are ordering a new replacement sever. This purchase is made possible by generous donations from SETI@Home participants."

Hopefully everything will be up and running smoothly again soon!