I love the unibody. I've watched the video of how apple machines the unibody from a solid block of aluminum. WOW. I have two, one from Nov 2010 and one just bought. I admire these laptops almost as if they were works of art.
So, when I got ready to sell one of them, and cleaned some dirt off with a moist cloth and a bit of soap, I was not looking forward to discovering that there's is a dirtly little secret I didn't know about:
Unibodys have some sort of coating, and that coating came off with a bit of moisture and soap. It changed the finish and created opaque, matte, whitish stains on parts of my unibody - just like when you rub paint off a plastic product.
If it ever happened to you, you will know what I'm talking about.
I'm taking it to the apple store tomorrow, see what they have to say.