The NFL set up "Super Bowl City" in downtown San Francisco, and naturally there is a lot of security present. The area around the Embarcadero has been shut down to traffic, and there is a significant security presence.
Wired put together a rundown of just the surveillance presence in place for the week. Government officials spoke to them, but obviously would not get into any specifics. The Department of Homeland Security classifies the Super Bowl as the second highest special event classifications. The 2002 Super Bowl was rated at the highest level (assignment usually reserved only for presidential inaugurations) because it followed the 9/11 attacks.