I used Yahoo Personals, which is no longer up. I met three women, and each encounter had a worse outcome than the one before it, so I decided I'd better quit before the next one killed me or got me thrown in jail. It went like this:
First one: No romantic chemistry, but a pleasant evening out, and I would have been open to a continued platonic friendship but I didn't hear back from her. (No harm done, nothing to discourage trying more.)
Second one: It was clear to both of us on sight that there was not going to be romantic chemistry. I would have still gladly gone through the whole planned evening (dinner, theatre, maybe a drink afterwards) as friends, but she saw fit to fake a cat emergency right after dinner and run off.
Third one: It seemed clear that we had the material for an excellent casual platonic friendship. We didn't have any romantic chemistry but we had a lot to talk about, including personal and emotional topics. Unfortunately, I got so comfortable with this that I told her about my fetish life. She sat quietly for a few minutes, then explained why she needed to be up early the next morning, and sailed out into the night. She made it clear on a blog entry that she was now afraid of me, and she later warned me that if I ever tried to contact her or stalk her, she would have me prosecuted, and that she had friends in law enforcement who were well aware of her concerns. (I refrained from writing to her and commenting that she obviously thought I had no rational thinking abilities whatsoever, if she thought I could possibly be interested in contacting her or stalking her after this.)
All this aside, I have this for an assessment of online dating: the more offbeat you are in your style and appearance, the less it makes sense to use these services. I'm not saying there aren't offbeat people on there, it's just needle-in-a-haystack that they'll be offbeat the same way you are, so you're better off getting off the computer and going out in the physical world and meeting people. The best way to do that is to pursue the things that interest you, in such a way that you meet others who share your interests. The more of a social conformist you are, the more you fit in and blend in with cliques and crowds, the more likely you are to find what you're looking for in the personals.