Actually it is starting to work on SF: with 1000s of new units, my apartment is now 20% lower rent vs this time last year.
I keep an eye on rents in SF and I've definitely noticed the trend downward over the past year or so. It was common to see 1-beds go for $3000+ and now most seem to be in the high $2000s.
Just my observation so I didn't know if it went as far as people renegotiating their rents down yet.
Edit: Just took a look at units in the Mission. Holy crap are there a lot of them (124 1-bedroom units). A few years back there were maybe ~20 max at any given time. Lots of new buildings and recently renovated. Even units in prime locations (close to Dolores Park) are sub-$3000 (although not many).