Quirky and fun
Scenesetter: on our US trip we looked for unusual accommodation with a bit of character.
Hotel Vertigo stood out for us because it's where Alfred Hitchcock filmed his famous thriller of the same name. Apparently Kim Novak actually lived at the hotel during filming. The movie plays on loop on a screen in the foyer, and the quirky furnishings add atmosphere. The hotel is also a reasonable price for SF.
We stayed twice at The Vertigo, when we arrived in the US and before flying out; we chose to return there based on our first booking, so fair to say we really liked it.
The good things: 
* Nob Hill location is pleasant and convenient
* Vertigo is a short walk to the CBD incl. Union Square and Chinatown
* some very nice restaurants nearby, ask the staff for recommendations (thanks Sean!)
* hotel is old of course, but recently refurbished in funky orange, chocolate and white 
* rooms are a reasonable size and clean; beds comfy
* bathrooms are clean and roomy; configurations vary, some have baths, others enormous showers. Toiletries are good.
* wifi is free and very fast
* there's a computer downstairs for guest use, and we saw it being frequently used.
To watch: 
* no onsite parking - but several garage options available within a block
* we had NO problems with our bookings at all...
* however, we spoke to two different guests while waiting in the foyer, both of whom had made a booking but found themselves without a room. One told us about how she was re-booked at another hotel owned by the chain that owns Vertigo, but it was in a less savoury area and she felt unsafe there. TIP: phone ahead to confirm your booking on the morning of your arrival.