Most people usually find their mate by chance encounters in living
their daily lives. IE. work, parties, 2nd degree acquintances, etc. So
why not have a type of dating site that increases the likelihood of
these chance encounters? ie, use collaborative filtering to find out
people you are likely to be good matches, then make suggestions like
"oh, their twitter says they'll be attending a christian fellowship
meetup tomorrow" (or whatever). Maybe even say "this person is a
friend of a friend of yours that you might not have known about". This
can give girls some comfort that the person is not an axe murderer or
something.

(reply related to above message) An online dating site that uses
collaborative filtering on large datasets of people (perhaps using
Facebook as a dataset). Then inform potential couples when they are
physically close to each other via cell phone/geolocation.

A similar article:
http://www.pcworld.com/article/id,137254-c,webservices/article.html