Of course it's going to get warm while charging, even more so if you're using it during the process. Have you noticed it getting significantly hotter than it used to? Or, is this your first notice of it?
I remember my Touch Pro used to get pretty warm while charging and using it...I mean, if you're really worried about it take it to a store and see what they say. I wouldn't worry about it too much as long as you don't start seeing erratic behavior from it or anything.