Clicking through a few times to http://blog.sfgate.com/cityinsider/2012/05/17/after-a-lull-s..., 2011 is apparently an anomaly, and around 20-25k new units (net) were added over the past decade. In addition, 2k new units were approved in 2011. Still not too high, admittedly (a 7% increase in housing stock over a decade).