Cannot believe the value - wonderful!
I stayed at the Chancellor Hotel for 5 nights in Dec- Jan 2011-12. It was wonderful. I picked based on trip advisor. I don't know how anyone has ever had a problem with it - it exceeded my high expectations.
I cannot really add much to what has been said. Rooms are perfectly adequate in size. Bed, television, chairs and a little room for your suitcase. They're not big, but if you've been to Europe, they're bigger than that. I requested a view of union square up high - was aware i might get a little noise but the windows block a lot out (except for the San Francisco noises you want to hear, like cable cars and soft bugle playing!) and this stopped by the time i was headed to bed. I had a lot more noise on the out skirts of New York. Also the view of Union Square was wonderful, and I loved knowing where I was. I was on the 11th floor but up higher might get an even better view.
The quality of housekeeping and furnishings is excellent. For the price I was blown away by what we received. The service from staff was the best I received from our stay. Check in, check out, porter, tour desk, everything was great. Yes the bathroom is small, but I don't know who wants to spend time in their bathroom. 
I will stay here again in a heartbeat and recommend it to anyone who wants somewhere clean, central, not too expensive and focused on making the experience great for guests. Location cannot be beat. Public transport in SF is incredible. I was able to shop as a young female on my own into the evening because we were so close to the stores and a lot of foot traffic around. Really hope that the Chancellor doesn't change - the price, the quality of service and the rooms are everything I hoped for.
Tips: 
1. We requested a fridge as soon as we arrived and it was delivered promptly. What a great free service!
2. The tour desk sells MUNI passes - we got our moneys worth as the hills of SF are killer, and sometimes it's very easy to hop on a bus/trolley.
3. The cable car stops basically outside, but at peak tourist time (or at least when we were there) the line up to get on them is insane, so we didn't try to use it. 
4. You can catch the BART to Powell St station for $8.10 from the airport - pretty cheap if you're on your own or in a pair. That said, it's about a 7-10 minute walk up a gentle-moderate slope with tourist traffic and lights. It is certainly doable, but I had 2 suitcases so it wasn't a stroll in the park. But if you're able bodied and want to save money, do it.