I had a powerbook g4 before and the case got seriously deformed when i put it in my laptop bag, so i have always wanted a hardcase for my aluminum machines since. I just got the spec hard case for my macbook pro and I think it does the trick. It hardens the whole structure of the machine, hopefully making it harder to crush.
Here is the URL:
SeeThru Hard Case for 15" MacBook Pro
In my case, my laptop bag is a backpack and if i put some books in it, it crushes the laptop. My solution was just to not fill up the bag, but now i think the plastic case would work.
as for heat, there doesn't seem to be any difference with the case attached or not attached. It doesn't look bad and it solves the "slippery" aluminum problem.
(I'm posting this in response to some of the threads I've seen on here about this case and hard cases in general).
cheers,
zgzg