This chart, which is (thankfully) easier to read easily depicts the drop in volume for 2006.  While you can see the drop is significant, it certainly is not the slowest year we have seen in recent history.  In 2001 the total for the year, including those not on MLS, was 2676.  For 2006, as far as my research could turn up to date, 3191 residential units were sold.  Once the County updates their website, my charts will be updated with those homes sold off the market.

Source:  BAREIS and http://www.co.marin.ca.us/ and current rhrough January 4, 2007.