A very good stay in a great location
This was my second stay at the Hyatt Regency San Francisco. First was in August 2011, when I booked the hotel on Priceline ($165/night--which was very high, but it was an expensive time for some reason). This time, I booked on Priceline for $95/night (+ taxes) and was very pleased with the rate.
The Hyatt Regency is one of my favourite San Fran hotels. I've stayed in the past at Le Meridien (also booked on Priceline, $110/night) as well as the Hilton (on O'Farrell) and the Hotel Nikko. I much prefer Le Meridien and the Hyatt Regency because they are in the Financial District and not Union Square, which I find too busy for a vacation -- nice to visit to shop, but don't want to stay there.
The Hyatt Regency is great because it is right above the Embarcadero BART & Muni stations, making it easy to access from the airport on BART (one way, $8.10). Also easy to get around the city by transit from there, although it is so centrally located I usually walk everywhere in the downtown area. It is right across from the Ferry Building which has great restaurants, coffee shops and a farmer's market (and the ferries, of course). Also across the street from the Hyatt is a Walgreens and a Starbucks, both very convenient. 
The hotel itself is nice...the rooms are furnished modernly although in some places (carpets, hallways, etc.), it is a little rough around the edges. For $95/night I won't complain, but at full price I might expect a little better. However, it is a great hotel and that is a minor point overall. Internet is $9.95/day, but free at the Starbucks across the street. 
When I stayed in August I upgraded to a balcony room (+$40/night) which was great -- excellent view of the bay. This time I didn't upgrade, but I still nonetheless was given a room with a great bay view and a large window that opened. They certainly didn't put me in the worst room in the hotel as a Priceline customer. One thing I don't like about the rooms is that the bathroom sink/vanity is outside of the bathroom itself (this has been true for the double and king rooms I've stayed in). 
The hotel itself is visually impressive too, with its central atrium. Movie buffs might like to know that some of the lobby scenes from "The Towering Inferno" were filmed in the hotel lobby (the glass elevators will look familiar). That being said, those with fear of heights might be better to choose a different hotel (glass elevators and all hallways open to a central atrium...see the lobby pictures). 
An important tip -- try to avoid adjoining rooms. I had one during my first stay and it was like my neighbours were in the room with me. My room on the second stay was very quiet, except I could seem to hear the people above me walking around...but not a big deal. Very little noise from the atrium. 
Overall, a great hotel and even better when you can get it at less than $100/night!