Typing "how many mathematicians" into Wolfram|Alpha, yields the information that there are 3160 mathematicians in the United States. The source listed is the US Bureau of Labor Statistics, and this site in particular (broken link <s>http://www.bls.gov/oco/ocos043.htm</s>). That site contains such gems about our profession as: "Mathematicians usually work in comfortable offices."

Cool.

Edit: [newer link that isn't broken, yet][1].


  [1]: http://bls.gov/oes/current/oes152021.htm