I'm looking into buying one of the Apple branded Smart Covers for my iPad 2 in conjunction with a nice transparent shell. (I wanna show off this sexy beast!) I have a protective case on it with a swivel cover attached, but I find that sometimes gets in the way and would like something removable. My first and foremost question is are they interchangeable? Do I need to buy one specifically made for the iPad 2 or are the ones that work with the 3rd and 4th gens compatible? I heard that the Retina display added a slight bit more thickness to the newer models. Also, assuming I buy one, how sturdy is it as a stand in both modes, both propping it up and tilting it at a slight angle? Is it easy to tip over or knock down? When typing on it at an angle, will it stay folded up?