Per Brandon's point – It might be fairer to say that "no site would allow users to implement this kind of tracking on their own" – even then, I could imagine a site constructed EXACTLY around the principal of a user-side free for all, though I'm pretty sure I wouldn't want to visit the resulting site.
That said, I can easily imagine a dating site partnering with optimizely to help provide tracking and metrics to their membership in a convenient manner, without having to build that whole freatureset out in-house. Still, it would most likely need to be a white label agreement of some sort, as running the site dating through a third party like optimizely would break most TOSes for existing dating sites.
deano.com 