The most common problem that Game-Masters have to face is that of managing and maintaining the flow of the game and what to do if it stagnates. How to keep the campaign from running aground?
I think one of things the players in our long running play be e-mail Star Wars D20 game have accepted is it's slow pace. Sometimes things don't happen for weeks, even months if we're changing GM between stories.
I've found that game flow can be inversely proportional to the familiarity of the players. The more the groups I play in know each other, the more likely the are to chat and digress.