It was founded 2003. By the time it was founded, a lot of other professional sites were very good, I'm talking about dating sites. Also plenty of other sites were free with a lot of users and big companies made that sites. Why plentyoffish.com has become so popular?
it could be the interface, the success rate, or their advertising? They look pretty good to me if i needed a date, the success rate is really high and they have plenty of serious looking members.
probably a combo of things, he is a one man show, so it doesn't cost him a whole lot to stay in business, while others could have fallen off trying to keep up with salary expenses etc..