Your diet should consist of a mixture of glucose, fats, proteins, and other nutrients.
Your question is a little vague. The sugar in fruits is glucose. What do you mean "in excess"?
I don't see any problems eating a ton of fruit. If you are just consuming fruits entirely for your whole diet, then I would say that would be in excess. As long as you are incorporating your other nutrients your body needs, it shouldn't be a problem.
edit: actually, I should correct myself. The sugar in fruits is actually fructose (and some fruits / vegetables contain cellulose...but I haven't taking nutrition yet). I don't think there is a big difference between fructose and glucose, but I will do some research.
edit2: Another thought. The more sugar / glucose you eat, the more of that enters your blood stream. Your body has to produce more insulin to help maintain the level (basically, your blood would turn to syrup if it doesn't do this (very crude example, but you do get the point). Some research has indicated that eating "excess" (I hate using this word) sugar (glucose) has shown an increased risk for diabetes. I am not sure if this applies to fructose. Sugars in soft drinks was an example used in the study. I'm not sure what sugar is in soft drinks, but I imagine its glucose.