I went from a Powerbook to a Macbook to a MBP and I can honestly say that the aluminum palm area is much easier to take care of compared to the plastic.
True aluminum dents easier, I lightly bumped the top of my powerbook while I was sliding it under my bed and it got a tiny dent, while my macbook fell about 5 from a tabletop and landed on its lower right edge, it came away with only a slight scuff on the case which was buffed out in a couple of minutes.
The one thing that I do really miss going from the macbook to the MBP is amazing wireless reception range of the macbook. I guess this is less of an issue if I got around to picking up a wireless N router.