I would like to try priceline or bidding for travel for a hotel in San Francisco but I am not familiar enough with the location zones. Can anyone fill me in on the general characteristics of them? I want to stay in an area safe enough to walk around until, say, midnight, and close enough to public transportation so that we don't have to rent a car to see the city. Any suggestions?

In short, I would recommend either Nob Hill or the Marina. Some of the area around Embarcadero would be ok as well.
These would be the "safest" (relatively speaking), are quite close to public transportation. I'd say Nob Hill (Mark Hopkins,Fairmont,Radisson Stanford Court)is a good bet on priceline or bidding for travel. Of them all...I say go with Nob Hill. If you can get in to the Ritz Carlton try that. It is midway between Union Square and Nob Hill.

Pacific Heights is a beautiful and charming neighborhood with lots of character and walkability. Probably an inn is the way to go since you're unlikely to find the big hotel chains; I guess that's part of the appeal. Anyway, you can't go wrong here.

I stayed in Union Square this past August. I had read alot of negative posts but found the area to be very safe and convenient.

While "safe enough to walk around" is something of a subjective issue, I'd probably be inclined to limit my bidding to the Union Square East/Embarcadero and South of Market/Embarcadero zones initially, at the 4 star level, maybe the 3 star level too, provided you don't end up with one of the "boutique" hotels that seem too often end up being just old and small. The 3 star hotels around Fishermen's Wharf would probably be okay too.

The concern I'd have with the Union Square West zone is that you might end up with the Hilton, which has had a spotty (to be kind) group of reviews at BFT. Its location is okay (close to restaurants and shopping) but then most of the downtown hotels fit that bill.

Make sure you bone up on bidding strategies at BFT before you commit.

Since parking at most downtown hotels is $30 per day or so, you can log a lot of minutes in cabs, never mind the bus, trolly, cable car, BART etc., even before you start paying for the car rental itself.

Sorry, I meant the "South of Market - Convention Center" zone.

Walker,

As a lontime resident of SF, I will advise you to not stay in Union Square, or Downtown SF in general. At the end of the workday much of downtown basically shuts down and is not all that safe. Other neighborhoods mentioned are okay.