I've been a several long distance, 2 ended in failure (duh!) and I'm currently in one but I see him most weekends (3 hours apart). We gchat/skype everyday, and some days it can be only 15 minutes if one of us has a lot to do, on other days, it can be 2 hours.
With my previous LD, I would say the one thing that made it fail was I started feeling resentful that it was one-sided. I was paying for the plane tickets to go see him, and always the one calling, not the other way around. The first one bought me a tiffany bracelet for an anniversary even though he knew that I did not care for jewelry and I never wore it. In my current relationship (2+ years, about 9 months LD right now), we take turns driving to see each other, and he makes a lot of effort to call me, cook for me, and we take turns paying for meals out, movies, etc. So, it's more equitable. I will be abroad for a year from summer 2013 - summer 2014, so that will definitely test our relationship.