http://www.wired.com/culture/lifestyle/commentary/sexdrive/2007/04/sexdrive_0427?currentPage=1(Not really _not_ safe for work, but the title does prominently include the word "SEX" in large friendly letters.)
An interesting commentary on the psychology and sociology of sexual behavior.
A possibly revealing pair of questions:
(1) Would you describe yourself as "normal" to your friends?
(2) Would you describe yourself as such in a personals ad?
Update: I wasn't really trying to get people to answer the above questions, but the nature of the responses is interesting. I'm completely unsurprised that some of my friends would happily self-identify as "not normal"--hell, I would.
But that just comes back to the original question from a different direction: what is it that people are trying to convey when they say "normal"? Why do the people writing those ads feel a need to reassure their possible respondents that aside from their kink, they're "normal"? Why do some of my friends and I think that it's cool to _not_ be normal?