I've never traded in to the Fairmont (or stayed there), but I used to live in SF and wanted to point out that the Fairmont is not walking distance from Union Square shopping or near the trains to Fisherman's Wharf.
It is in a really beautiful area near Nob Hill and is walking distance to Grant Street in Chinatown and North Beach. I also don't remember it being close to any BART or MUNI underground station, just the MUNI buses. The MUNI buses are rather slow if you take those around the city.
Just FYI, in case being "centrally" located matters to you. It's a little bit harder to get to than most hotels in SF. It's best to take cabs or to have a car if you're staying in this area (but parking fees are outrageous in SF).