We were there for 3 days recently. It's not as nice as I remembered it from overnighting there on our return from a trip to Oz, but it was OK. Nothing special, but no problems either. We were at a very cheap rate. They gave us a C-Level room, which since we weren't doing a convention, was all we needed. The lounge is closed over the weekend, but we were given breakfast in the restaurant. We were pooped enough the first night we actually ate in the hotel restaurant, which was hardly brilliant but more than good enough for tired and hungry travellers. There are other restaurants within walking distance, but we didn't find anything special. The one across from the Marriott is at least not a chain; it is a throw back to the early '80s (a sort of Olde Englishy steakhouse); it did seem to have an enthusiastic local clientel - we ended up having an appetizer in the bar because the menu was Cow and More Cow and I couldn't face it. Sorry I can't remember the name, but you can't miss it.
What was handy is that we were able to have our meeting with people from San Jose and do some actual touristing in San Fransisco proper without having a car.
If you get in early enough, you can easily take the shuttle back to the BART station at the airport and go into SF for something really interesting for dinner.
The airport shuttle bus serves both the Hyatt and Marriott, so keep that in mind if you're timing your trip back to the airport to catch your plane. The Hyatt comes after the Marriott on the loop, and that can add a fair amount of time to the trip.