Straight male here. 27 years old.
Straight, female, late 30s.
I’ve used Match and OKCupid. Met two guys that didn’t work out through Match, and OKCupid yielded one that’s still working out a year and a half later. 
I’ve done them on and off since about '98. (straight female, 40 this year) I first used Yahoo and I tried Match but I found the most interesting people on Nerve.com which is the same personals site used by the Onion, Salon, some alternative weeklies etc. I did try OKCupid a couple of years ago but there weren’t many people my age on it.
I’ve been on a bunch of dates but never clicked with anyone which, to be honest, is probably more about me than the guys. After I turned 35, the respose rate to my ad dropped way off and I’ve kinda stopped looking becasue I’ve been frustrated with a lot of pleasant but not interesting dates.
I’ve been using OKCupid lately, and it seems pretty decent. First date was pleasant but boring, second date was fun but the guy was ultimately not my type, and third date - I just met the guy for lunch today, which I guess was our second date. I like OKCupid’s matching system - it’s accurate as far as common interests and life philosophies go, I think. Whether you’ll share a spark when you actually meet up is an entirely different matter.
Female, 25.
I used love@aol ages ago, before it merged with match, then I used match. Had a bunch of dates, then met The One. Been happily married for 4 years. I’m a guy, 37 years old.
My older brother is currently using Plenty Of Fish, and from what he says (I think he used eharmony first), the whole thing has changed a lot over the last several years. Now a lot of the pay services try to lure you in, and let you get spammed with russian and other emails (my brother’s friend apparently got strung along by a woman that apparently worked at eharmony–out of the country, but whaddya know, she’s coming back in a couple weeks, right after his term expires, so he has to re-up to continue the dialogue. That sort of stuff).
Straight male. I’ve tried Match.com and have gotten a pretty impressive bupkis. I’m not sure if I’m just a rather specific sort or what, but no replies to any emails or winks or what-have-you.
Bi Female, early twenties.
I’m having fun on OKCupid. I’ve met quite a few guys, but not many women at all. I’ve met four women in person, and one was boring, one was crazy, one is a sometimes friend now, and one is straight (but she kissed me last weekend). I’ve been on there for six-ish months now. The guys? Well, a few here and there, and I’m seeing two very nice, very fun guys right now, and have met/gone on a few dates with six more, I think… And am kinda chatting friendslike with two more. But then again, I’ve gotten stood up by two, and hit on by a bunch of guys that are so not right (some not right in the head, some just obviously not right for me).
I like getting introductions online and then meeting in person, though… I’m not big on internet courtship at all.
edited to change: forgot a one-date guy
One of my best friends is getting married to a girl that he met on Match.com. He had just moved across the United States for a job and didn’t know anyone. So he joined looking for friends, met a great girl, and 3 years later they are engaged! Not a bad deal 
It can happen!
Just got married to a guy I met on okcupid. We’re both in our mid-30’s. It’s brilliant because we lived within 45 minutes away from each other for 10+ years but never met, and never would have if it weren’t for the internet. Couldn’t be more satisfied with it, obviously.
I’m a single guy, who is apparently the worst auto-bio writer ever. My friends all tell me that the girl that “lands me” is very lucky. I’m a fairly different (read: less combative) person offline, than I am online.
I’m nowhere near ugly, but I’m not exactly enthused about my looks. I hate that people are concerned about looks, but it’s life, and I’m guilty of it as well. Ah, the dichotomy.
The fact that HazelNutCoffee is single, tells me that most guys (in Chicago at least) don’t know what they’re doing. She is, well, super cute, beautiful even. I’ll stop, no need to get creepy.
I have a slowly-gathering suspicion that the online world is oriented towards people who younger than forty.
Or maybe it’s just me?
I just think it’s oriented toward non-me people.
I’ve been very happy with Match.com–that’s where I met my current sweetie, and it’s been over a year now. But I found Match was surprisingly easy to find dates, at least in a large metropolitan area. I’m a very average looking guy, so I just had fun with my profile to set myself apart from other guys and it seems to have worked. My profile was a bit off-the-wall and sarcastic, but it was very self-selecting. The girls who got it would have a pretty good chance connecting with me. Oh, and I included pictures that looked casual, but showed a head shot, a three-quarters view, and a full-body view.
So I think it’s important to show a spark of personality in the profile, without getting too involved and wordy. Put in some basic facts that leave questions open for conversation, that sort of thing. Also, my rule for reaching out to another member, is to keep the introductory email fairly short and sweet, including some point of conversation that indicated you read the other person’s profile. And, if the initial emails go well, meet that person within two weeks of first contact, if possible. No need to get wrapped up in some torrid emotional email crap only to find out you don’t click in person.
I’m a straight woman, 35, and over the years I’ve tried Match, Yahoo, The Onion (which isn’t the same since FastCupid took over from Springstreet), and OKCupid.
Even though OKCupid has the fewest men my age, I’ve had the most success there: a few dates, one 3-4 month relationship, and my current relationship (8 months and counting, with plans to be living together by this time next year).
One thing that’s important that I don’t think anyone has mentioned yet: BE PATIENT. I was off and on the various sites for years before I met my current SO. Could just be me (of average looks but somewhat-above-average intelligence and eclectic interests), but it might take a while. If so, hang in there! Oh, and I second everyone who has stated a preference for meeting in person sooner rather than later: no amount of online “connection” can make up for zero chemistry. 
Straight guy here.
I tried okcupid for a bit, but didn’t have great matches there. Each girl seemed to want to be more alternative than the last. It was a bit too much for me. I then signed up with eHarmony, and had much better success. There were tons of matches, and good matches, too. Since users have to pay to get the real benefits of the site, it seemed like people put more time and effort into their profiles, and just seemed more “serious” (this may or may not be what you are looking for in your dating life, of course). I met a wonderful girl there and we have been dating for six months now. She’s the girl of my dreams.
There’s another thread around about whether online dating still has a stigma. I’ll admit that I was one of the people who thought it odd, or thought that it wouldn’t work for me. With some time and effort, it has worked out better than my wildest dreams, and I am not afraid to admit that I was wrong to put it off for so long because of a perceived stigma.
I used Match.com for a while. What I hear is that a woman with a good photo can get a lot of messages on these sites (including a lot from guys who aren’t anything like what she says she’s looking for), but for men it can be a lot slower. I put up a profile and tried messaging a few people, and didn’t get any responses for about six months. From what I hear this isn’t that unusual – women who get a lot of responses don’t bother to answer them all, and some people put up a free profile out of curiosity without ever responding to anyone.
Gradually I tweaked my profile and tried different approaches to the initial e-mail, and eventually I got better at getting responses and even had some women contacting me. I got about five first dates in a couple months, about half of which made it to a second date and one of whom I ended up dating for a few months.
After she and I broke up, I met another woman online, although not on a dating site. We met on a message board (not this one) where we both had a profile that just listed our age and location. We both figured “What the heck, here’s someone my age who lives around here and shares at least one interest with me” and started chatting with each other. Now we’re married, so go figure.
I’ve been on Match for a while. I’ve had a lot of dates, some of which have resulted in good friendships. I’m sorta’ kinda’ seeing a woman who I met not too long ago through Match – cute, smart and creative – but still corresponding with a few others.
I have an “anti-profile” - I mock the cliches one usually finds in online profiles and don’t really try that hard to sell myself.
As others have said, don’t put all of your eggs in one basket. Don’t depend exclusively on online dating to create a social life.
To be fair, I have actually had some success on OKCupid, such as it is. I met one great guy there that I would be dating now if he weren’t in a faraway state, and another localish guy who seems cool, that I went out with this past weekend and am now freaking out about whether to call again.
I met my boyfriend on Nerve. I’m a straight woman, 32 years old. We’ve been dating for almost a year and are moving in together at the beginning of September. I hated writing up a profile and all that crap, and finding a photo that was honest but also flattering. He was the only one I went out with of the guys who e-mailed me, and obviously we hit it off.
I’m a 25 year old bi male and use OKCupid. I met a girl that I had a sort of friends with benefits thing with for a few months a couple years back but haven’t met anyone else on the site, though I did have a month long email and IM correspondence with a guy in a nearby city earlier this year. I very rarely initiate conversation and the few people that have contacted me all drift away or lose interest pretty quickly.
And just for the hell of it: my profile.