Sometimes when I tap my ipad screen the icons or links or whatever will not respond to my touch! Repeated tapping may help but not always. I do a lot of work with my hands and my finger tips are pretty calloused. Occasionally there is glue or paint residue on my fingers, but I try to keep my hands clean when using the touch screen. Could callouses and / or thick skin be the reason for this lack of responsiveness? Is there any work-around? Thanks!