Yup, I've had a white Macbook and a silver Macbook Pro and both were in mint condition when I sold them. My sister-in-law has a silver Macbook Pro and it looks terrible - scratches, dents, dings all over it (it's the older style aluminum, pre-unibody). Cases = win.
iSkin makes some good rubberized keyboard covers that you can actually type on:
http://www.iskin.com/protouch_macbook/common_features.html
One of my professors had one...I've always hated keyboard covers, but this didn't block typing at all, somehow.
One other thing I've tried is the microfiber wristpad protectors:
http://www.marware.com/products/MacBook_2/Silicone-Protection-Pack
They were nice when I had a white Macbook - kept it from getting too dirty. Dunno if you'd need them on a metal unibody.