Jacques Steinberg of The New York Times has a good piece on how students should approach the application section that asks for a list of extracurricular activities.
He quotes Monica C. Inzer, the dean of admissions at Hamilton College in New York, and member of the Common Application board:
We’d rather see depth than a longer list. I think students think we want well-rounded kids. We do. But we really want a well-rounded class. That could be lots of people who have individual strengths. Distinction in one area is good, and better than doing a lot of little things.