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These weren't smudges, definitely scratches in the aluminum. I went to the apple store and they replaced it :)

Wow, that's pretty outstanding customer service.

I used the clear tape trick.

Yep, I used a strip of clear packing tape on my spine where the SmartCover contacts it, since I was kind of aware it's a possible problem.

Now I'm using an iCarbon rear cover, ultra minimal (basically just scuff/scratch resistance, 3M faux carbon laminate), but it does cover the contact point so no concerns :) I also take my Smart Cover on/off almost daily (easily more than once), so that increases the chance of a scuff.
 
That's a relatively common problem. Apple replaced mine, no questions asked.

Upon buying my iPad 4 I chose the Smartcase.

It's ideal as there's no way it will cause damage. It's also very nice to have the back of the iPad covered for a very secure grip with a comfortable tactile experience.

Although its nothing more than speculation, it seems to resist scratching & scuffing better. Mine still looks as good as new.
 
I have seen a s***load of iPads in my time, and I've seen this issue of the actual denting/whatever of metal very often, but only on black iPads, never a white iPad. I don't see how that makes a difference, but from what I've seen, it seemingly does.
 
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