As my data structures professor would say: "Bipartite matching is a hard problem, specially when it involves women!"

Seriously, though...

IMHO the most successful dating site would probably start off as a Linked In like social network, where you could have matches based on the people you know. Matching algorithms of any sort (like Match.com Chemistry.com eHarmony.com, etc use) could be used to improve the matches, but I think that having a "recommendation" from people you already trust would be a very big plus. This is probably why pre-existing social newtworks like Facebook, MySpace, Hi5, et al usually end up being used for such purposes.