I have bought two speck see thru cases
On the MB's, at least the white, you wont notice its there.
I have one for a mbp, I put it on, and after a year, I forgot its on there, i just realized the other day in the apple stores when i felt the mbp's smooth case. It never scratched the aluminum. It wouldnt make a difference, nice either way. Though, when i take it out, it feel so fragile, so, i say get it, and if you don't like it, trash it, i don't think its that expensive, or you could sell it on ebay.