I heard about this about a month back for a used iPod i bought. I did it on my iPod, it cleaned it really well. Did nothing for the scratches.
I had an old macbook battery that i had to ship back to apple so i thought i should test the Brasso on my macbook battery and see if it did anything to clean and remove scratches.
Well, it cleaned it, i was light with my fingers. I don't THINK it scratched it more, it might have not scratched at all, but i cant be sure since it was kinda scratchy already.
I cleaned my G3 ibook with it all over, as well as the power brick. It made no scratches on those, but i think the cases are different material.
again test it somewhere you can handle a scratch or two, like the bottom or side, i dont think it will do to much if anything.
Also, i used a microfiber cloth with my brasso. Not a normal cloth. It did clean it really well however.
Good luck, let me know how it works