We had a private room in the annex for 5 nights.
The annex is very well situated, just enough close to the main building to walk and have your free (and good) breakfast, but far enough of the street to be a quiet place.
It's a small building, just behind a school yard.
Our room (108) was ok, pretty large and bed was comfortable.
BUT: Putting the washing machine and dryer at the door is not very smart: very very noisy (you can wash your clothes until 10pm... too late after a loooong walk day in SF)
Also, putting garbage at the window is not a good idea too... when it's warm and sunny if you want to open the window, well , you can imagine...
Shared bathroom was clean and bed linen also clean.
Fully equipped kitchen was great too, but no table to eat in the kitchen (no table in your room also.. just on the top floor but evenings are quite refreshing in SF!): Why don't you put a kitchen bar along the window, it will be perfect.
After All it was a great deal. Very well situated, cheap (for SF) and staff in the main building was cool.
Go there, you won't regret it!