If you can make it work, than it can be more of a positive experience than a bad one. However, they aren't for everyone. There's a huge trust factor when you can't be around the person you love every day, or even often. It's very difficult and you have to both be very mature people who truly love each other and want to make it work.
I've had more than one and they are tough. Not for everyone. You have to see the light at the end of the tunnel. Of course it didn't help that I had mine when phone calls were expensive and before webcams/internet.
I had one and even though we really loved each other, it was too hard (he was from Europe and I am in Canada). After three years of heart stretching we ended it. I like love making too much and I think that life is too short to spend half of my time waiting.
I'm in one. I've known (in person) my partner since last March (at same school), started dating last October (already distant). If we're lucky, we see each other once a month. They are definitely not for everyone, my sister can't handle a summer of distance even with visits. They are hard but for me, it's worth it.
I'm sure they work well for some, especially with today's tech, with webcams and face time, email and sms, etc. but I don't think I could handle the extended period of time with no skin to skin contact.
I'm in one and I have been in another long distance relationship before my current one. The first one didn't work out, but the current one I am in with my Dom is going swell. It is definitely not easy, but if both parties are willing to make it work, then it can last a very long time with few complications. It is definitely not the kind of relationship that everyone can manage, though. It's a good thing that my Dom doesn't live far from my city, but He has lived in my current city for most of His life. It's much easier for us to meet than it would be if He lived half-way across the country.
Been in one for 7 years. If you find that person you love more than anything else in the whole world who loves you back just as much, and you're both willing to work for it, it's actually not so hard. I'm very, very happy with him.
Also I didn't get to meet him in person for 5 of those years and people were very critical of the whole thing. Honestly, people's constant rudeness about it was one of the worst things for us. But when we met, it was absolutely amazing!! So far we've spent about 8 months together and we love each other just as much in person as we did in the video game where we met.
P.S. In case you're curious, we have lots of webcam and phone sex and we send pictures. It helps make the needing sex less bad. . . Nothing helps when you need cuddles, though. :\