Rents fell in 2008. I can tell you this for sure, because I had just moved to SF, and landlords were making deals. My landlord lowered my rent by $100 a month in order to keep me from moving in 2009.
Even as late as 2010 this was happening. I looked at a place on Russian Hill around that time, and it was offering rent incentives.
In my recollection, the market didn't pick up again until around 2012, corresponding with the rise in startup investment.
The data seems to back you up, so I stand corrected. [0]
I was basing it on my own experience pricing the rental unit I've managed in Berkeley for the last 21 years. Each year I do a rent survey for the East Bay, and that was based on my experience there, but the East Bay is a little less price sensitive in both directions compared to SF, so that's probably the difference.
Even as late as 2010 this was happening. I looked at a place on Russian Hill around that time, and it was offering rent incentives.
In my recollection, the market didn't pick up again until around 2012, corresponding with the rise in startup investment.