Big Hotel, close to Union Square
There was a massive convention going on this past week in San Francisco. The Hilton actually had some of the convention sessions being held in the hotel, as part of the convention. It was busy!
My husband was there on business,..I joined to sightsee and shop, and visit a few wineries.
We had a room in Tower two the first 2 nights, as we needed a larger room with two beds, ($100 more a night-and the rom wasn't great) in case a friend needed to join us for a night. 
It was an older room, not recently renovated. They no longer 'do' minibars in this hotel, so there is no fridge at all. The cabinet which used to house the fridge is just a locked cabinet now.
We moved to tower 3 for the remainder of the visit, since we just needed the one bed. Much nicer room, smaller, but newer. The parking garage is in Tower 3, so if you have a car and need parking ($47 a night, with in-out) this is a good room choice. 
They accommodated our room change, and helped me with the bags. 
This hotel is walking distance to shopping and the financial district. 
It is on the cusp of not great/sketchy neighbourhood. I walked to the Whole Foods up on California St, near Van Ness,..and quickly felt uncomfortable, such that I headed up, rather than west.
I have stayed in the Nob Hill area before, and closer to the financial district, both which are nicer areas and close to the Ferry building, etc.
Overall nice hotel, (Tower 3) friendly staff. 
***It's a surcharge for wireless in your room which makes me crazy, if you have read my reviews before. It's 2012, you need to offer free wifi instead of gouging traveller's at every turn. 
I stayed at the Hilton Garden Inn in Napa..(just as expensive at $309+tax) and wifi is free.