I've used them. Actually, the majority of the dates I've been on were with people I met online, including my fiance. I didn't do the eHarmony type stuff, though. I'm cheap.
Also, I think it's stupid that you have to pay them before you even get to look at your matches.
Try OkCupid or PlentyOfFish. Those were the better ones I was on, in my opinion atleast, and they're free. And there's plenty of people on there who are looking for booty calls and short term casual dating, not just the long term stuff.