I have/am using OK Cupid, I have also used Plenty of Fish in the past as well. Really it is a lot like meeting people off line. You have to sort threw a dozen or so crazies before you find a decent one. I think it works well for people who are shy (like me) or people that just need a change to their social circle. Also it is what you put into it. Half ass your profile and your emails you send to the person and you get half assed back. But time and thought into it and it will pay off eventually.