The problem with dating sites (like social network sites or internet messengers) is that the utility you can gain from it is VERY related to how many other people are actually using it. This means that there is a natural drift towards a monopoly. Nobody wants to join a dating site that only has 1000 people. If you do not have a really good reason to think that your dating site idea will get off the ground, it probably wont.
One way you could possibly get past this is to match people up who do not sign up or even know about this service.
For example, you could create bots that browse okcupid, for answers to questions, ignore okcupid's stupid algorithms in favor of our own much better ones, and then send two people a message that describes how our service works and introduces them to each other.
Is this legal? If so, I wonder if okcupid would take stop it anyway.
How can there be a monopoly if people can use more than one dating site?
Unless OkCupid bans you from putting your profile up on other sites, you can just as easily put a profile on another site with less people, if the site seems promising.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.