I have the seidio and while it doesn't scratch the back it does scratch the chrome. You can always get this http://www.radtech.us/Products/bezel-blaster-iphone-scratch-remover.aspx and this http://www.radtech.us/Products/IceCreme.aspx
Seidio Innocase II
Basically an InCase slider, but has a felt lining on the back to prevent just this type of problem.
Seidio Innocase II is just as bad