Well, basically everything to be said has been said...but I'm gonna go ahead and state my opinions anyways. 

I'm 18, and I've been in a long-distance relationship (2000+ kilometres) since June last summer. This is the only relationship I've ever been in, but I love it so much. I met my boyfriend online when I was fourteen. We had a crazy amount of stuff in common, and became pretty close friends over the next few months. Then we exchanged Christmas gifts. And birthday gifts. And basically friend-zoned each other for about three years before he asked me to be his girlfriend. 

It's definitely something that can work, as people have said, depending upon the couple. We're both very easy-going people. So things that might annoy or frustrate the other person in an online relationship, they don't affect us quite as much. We're both incredibly accepting of each others differences, and on the few things we don't see eye to eye on, we agree to disagree. Someone also mentioned how a level of honesty was required in order to maintain trust....he once told another girl she was 'cute', after she had first complimented him, at some event where he was working. He proceeded to tell me about it the exact same day, just to be sure that I knew. I did the same thing when another guy flirted incessantly with me on the bus during the 16 hour drive home from a track competition. We're about as honest as it gets. XD

And yes, there definitely has to be that feasibility to meet up in real life. A friend of mine had an amazing relationship going with a guy a year older than her, until he graduated and went to school in the city. It was only an hour and a half away. But at the time, she didn't know if she would end up in the same city as him or not. There was too much uncertainty, and they mutually agreed to end it. 

So there's my thoughts on the topic. :)

For interest's sake, I'm meeting my boyfriend this summer. He's coming up to Canada for my graduation.