That's how I found somebody a long time ago, when I was 18 or 19. I personally don't have good experiences with it, because I eventually found out that the person I was interested in had some psychological issues. One time I simply forgot to log on to Windows Live Messenger -- even though I told her I couldn't be online all the time, I had a lot of school work and other work to do, and I told her I probably couldn't be online that time -- but she went bonkers nonetheless. Just because I was offline *one time*. I had noticed she was very clingy, but I thought nothing of it... guess I was a fool.
But, that problem is probably mine and hers, not that of online dating. Still, I think there's many weirdos out there on sites like that. Talking on the internet is often easy, there's less of an emotional connection because there's body language missing. People also can often search for exactly the right words and think carefully about everything, when in real life that might not always be possible. So in essence, you can make yourself look better than you are, less troubled, etc etc. But even that is different per person: some people don't think that much when they type, and I'm sure you and I both have had problems with highly emotional people on this forum. So in that sense it's a gamble.
I haven't actually ever dated in real life... I've never found anyone in my direct environment who was truly nice and didn't just 'act nice'... most people are just very matter-of-fact about everything, I've found. But, I don't go out much, and I suppose that makes it seem worse than it is.
Sooo... I dunno if it's better or worse than in real life, but I'd say there's many people who pretend to be somebody they're not, and you have to be careful. But I know it's possible to get good relationships out of online dating -- in fact, my mother found a really nice guy after her and my dad's divorce. They're still together and happy! It may be a gamble, but you've also got a bigger chance of spotting somebody who you feel attracted to. It's so easy on the internet -- you can find people who live miles away, even countries away. There's many people to choose from, so I'd certainly give it a shot!