Long Distance Relationships

Earlier this month Nathen wrote about long distance relationships.  As somoene in one, he wondered how to measure the difficulty of being in one.

It seemed to me, as someone who has been married a while, and has a little experience with marriage counseling, that Nathen was pursuing his idea backwards.

For example, he knows that free video chat and phone talks make life nicer for those in a long distance relationship, so his metric rewards having those luxuries.

I would, instead of building forward from what is day-to-day pleasant, work backwards from traits of successful relationships.  Here I'll need help brainstorming!

For example, someone wise (but I sadly have no citation!) coined the phrase emotional adultery to describe when a husband and wife are no long each other's best friends.  If the husband is more emotionally close and open with a golf buddy than his wife, that's still a huge weakness in his marriage.  Thus, for Nathen's discussion, I would ask if the couple in the long distance relationship had some way of staying best friends.  Free video chat and phone talks might be their solution, or perhaps they manage by writing letters, or perhaps they both have no social life and spend hours playing a MMORPG together.  Whatever their trick, it's the result of staying best friends that matters, not the mechanism used.

So I ask family and friends that have more experience with long-distance relationships than I, what threatens a long-distance relationship?  And how were these threats averted?