I have the newest Macbook Pro 15" (silver) and I am looking for something that stays on permanently and will protect it in my backpack and if it falls. I also want it to be as thin and good-looking as possible, and to keep out dirt. Right now I am comparing the Incase and Incipio hardshells. The Incase has rubber feet on the bottom- are those helpful or annoying, and are they there to compensate for a cover that is slick? Or is the Incipio case rubbery enough that feet aren't necessary? Thanks!