saying flat design is a danger to tablets is thinking wrong. They aren't thinking like a user, where all the pretty little pictures do something and you can interact in the tablet in new and exciting ways. We don't need a scrollbar to tell us the list can scroll, we should be able to figure it out by the way it runs off the page. We don't need a 3d-esque button to know that clicking on the box labeled "send" (or the little paper airplane icon) will ship off our letters. Everything is touchable and does something. If someone sits down at your app and doesn't realize that they can interact with the element, or tries to interact only to find out that they can't, flat design hasn't failed you - good Design has failed you.