Has anyone noticed excessive sweating while on Concerta?

Yes. My son was diagnosed with ADHD in grade school, and we prolonged giving any meds. until he realized how much it was affecting his relationships, grades, etc.
In high school, he tried a couple of the stimulant drugs used for ADHD treatment. He did not like any of them because he said they made him sweat like crazy, and have very dry mouth... typical of stimulants. He said the sweating made him particularly uncomfortable around the gals! So, he used them as sparingly as he could. The excessive sweating was helped by his football practice and playing, and by exercising in any way. It was important for him to stay hydrated and exercising regularly. That is typical, from my own experience. The stimulants do just that... stimulate the metabolism so that the brain is able to more effectively process the thought overload. I've heard this from others, as well... just one of the side-effects that will subside a little bit with time, exercise, and the body getting used to the meds. Good luck!