INC did an interview with Markus Frind where he talked about not necessarily trusting what his users wanted when it came to partners. He's got an algorithm that suggests people for matches even if they said they wouldn't be interested in the person:

... if you tell Plenty of Fish you want to date blond nonsmokers but spend all your time gawking at nicotine-addled brunettes, the program will adjust

(The quote is on page 4: http://www.inc.com/magazine/20090101/and-the-money-comes-rol... )