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I've got a red Speck Satin case on my MBP and I couldn't be happier about it. It's a great looking and feeling cover, and it definitely helps protect my machine from small drops, dents, dings and scratches. I wholeheartedly recommend this case for any looking to protect their Mac if they are as portable with their MBP as I am.
As far as your concerns, I havent had any damage done to the exterior aluminum of my MBP by putting on the satin cover. And while the case is a snug fit and can be difficult to take off, the bottom half of the case is much easier to remove than the half that covers the display housing, which proves extremely useful if I'm doing some upgrading to my machine or should it ever need to be serviced.
Get the Speck Satin case. It's definitely worth the money and is one of the less intrusive cases you can put on your machine.