What shuts down in San Francisco at Christmas?

[babsbunny]

I just noticed that hotels in downtown are half the price over Christmas compared to what I've been seeing for fall travel, yet airfare is very reasonable.  Any thoughts on if things will be open December 26-28?  Are there still things to do after dark (given that these are the shortest days of the year)?  Is the weather ok (above 45)?

I'll browse the other thread on things to do.  I'm more curious if things are open.

Thanks so much!