Because there's a GRIP of good breweries out there. And the WhiteLabs (one of three major yest producers for the brewing industry) testing lab.

Other than that, I'd recommend a daytrip up the way to La Jolla and a day in Balboa Park. Neighborhood out by the Gaslamp and the restaurant in the Sofia hotel were my favorite spots in the city. I'd also recommend checking out Chicano Park in Barrio Logan.

Also, sign up for car2go while you're out there. It's a pretty cheap way to get around the city without having the full rental car costs for a day (since you can rent point-to-point).