75% of SF rental units are rent controlled.
That sounds like too much.
Though, I don't think this is "rent control" in the NYC sense of the term where rents are kept way under market rate.
Rather, it seems to be a set of ordinances around what landlords can and can't do, largely pertaining to rent increases: http://sfrb.org/rent-ordinance
I don't think most people enjoy this benefit of rent control, it wouldn't make sense to rent out properties. I wonder what is the effective rent control rate (that which has affected price significantly). Maybe a rental turnover rate would hint at a solution.