The key to a successful GSoC experience is good communication. It is both a challenge and an opportunity. You are often dealing with students who have never participated in open source or collaborative development. Your mentors may be volunteering time they don't have. Neither may have worked across the time and cultural spans commonly found in GSoC.
It is up to the org admin to stress communication strategies and expectations for both students and mentors.
The number one reason why projects fail is poor communication. It is often the first sign of a project in trouble. Poor communication may originate as much with the mentor as with the student. A big part of your role as org admin is to lay out guidelines and advice at the start of the program, and then to keep track of progress. The org admin should be aware of communication problems early on. The only way to make sure you know what's going on is to periodically check-in with individual students and mentors. The week before evaluations is a good time to make contact and ensure there are no surprises coming. You should also stress to your mentors and students that they should contact you whenever there is a communication breakdown.