I came across this nice study the other day. The authors looked to see if there were any relationships between carbohydrate intake and body weight. Several factors were studied including carbohydrate amount, glycemic index, and glycemic load.
Controlling for the various factors, they found that daily carbohydrate intake and percentage of calories from carbohydrates were not related to body weight. They did find that the glycemic index of carbohydrates consumed was related to body weight. Again, it seems that it's the type of carbohydrate (those with a high-glycemic index), not the total amount consumed, that leads to health problems.