There was a misleading headline in one of the local real estate blogs recently suggesting that "Fewer San Francisco Homes Sold In 2013 Versus 2012". But the annual numbers reported in that post actually referred the full bay area, not just San Francisco. In San Francisco, despite tight inventory pretty much all year long, the number of residential sales in San Francisco was actually up by 2.7% in 2013 compared to 2012 (according to the MLS).
The post went on to say that December sales were down compared to the previous year (that also shows up in the MLS numbers) but it also said that the median sales price was down which is not supported by MLS numbers which show an increase of 11% compared to December 2012 median sales price ($849,444 compared to $765,500).
The actual differences of the number of properties sold are fairly trivial and it's important to note that the MLS numbers represent mostly resale properties and don't include most new construction sales. Nevertheless, the implication of the post was that sales and prices are slowing down in San Francisco which is not what the local numbers actually show.