eHarmony isn't successful because of the matching algorithm. eHarmony is successful because of the steep barriers to entry, perception of safety and privacy, its ability to attract women to the site, the rate at which they regulate match delivery, and the guided communication process.

The result is that you don't waste much time browsing profiles. You don't waste time trying to filter out spammers. You don't waste time coming up with clever pick-up lines. You don't get pestered by matches you close.

The matching algorithm definitely matters, but it's mostly a red herring. If I were eHarmony, I'd be far more worried about my terrible user interface than the matching algorithm.