Research in Edinburgh, Scotland last year, involving speed dates of 100 single heterosexual people (who then rated their dates), revealed that, in that context at least, the secret of a successful opening chat-up line is this:
encourage them to talk about themselves in a fun, quirky way.
Best line from the top-rated man:
If you were on Stars in Their Eyes, which celebrity would you be?
Best line from the top-rated woman:
If you were a pizza topping, what would you be?
One of the least successful lines (ahem) was:
I have a PhD in computing.
So now you know, if you didn't know before.
Now tell me, which one would you be if you were a New Blogger widget... blog template... JSON feed... Greasemonkey script... Linux distro...Symbian smartphone... oh yes, see, I'm definitely getting the hang of this!
(From a fun New Scientist 9 May 2007 article on "quirkology" by Robert Wiseman, who's written a book on the subject, done a podcast for New Scientist, and produced some YouTube videos.)
UPDATE: I went to an interesting talk on internet dating and how to write the perfect profile, at the Dana Centre - see my writeup of the internet dating talk.