I've had two experiences with long-distance relationships. The first was actually with the second woman I'd ever been involved with and still had feelings for. We hadn't dated for a while at this point, but when she was off at college, she decided that I was really the one she wanted to spend the rest of her life with.
We had a pretty serious correspondence going on (by written mail; this was before email was ubiquitous) and fun little packages and thinking-of-you trinkets going back and forth. It was a lovely time, like something you'd have in a romantic novel, and finally she came back from college and promptly decided, "oh, never mind." So, we never did manage to live out any of the various romantic moments I'd been planning for real.
The second one was quite a few years later, and it started with someone writing to me in email. It was just friendly at first, but it grew from there. She was very enthusiastic, writing me long letters several times a day and pushing for more of a relationship, while I was dragging my heels, telling her that I think we really needed to meet for real before getting too far into these things.
She made plans to come out and, abruptly, about ten days before the trip, suddenly didn't have time to write any more. She did show up and I ended up giving her a place to stay and driving her around, but she'd made plans to be with someone else. She was nice enough, but obviously it didn't turn into a relationship in person. The guy she did hook up with on the trip seemed like a great guy, though it didn't end up going beyond a fling for the two of them. He even came to a few of the parties I hosted in the years after she'd gone on her way.