Originally Posted by pstojanov
I'm sure that the metal chassis would be coated in a plastic to stop short circuiting. There's no way that metal would be left exposed with the possibility of short circuiting. I reckon the chassis is indeed metal coated in plastic and the the top layer is a coating which allows better heat conduction for cooling. It will no doubt feel metallic if it is a good heat conductor.
Actually, short circuiting isn't a problem because the circuit boards don't touch the chassis (they're on standoffs and/or have plastic sheets between them and the chassis) and the chassis itself is connected to "case ground" (ie. the ground signal of most of the laptop's electronics). You can get electrical continuity across the lid of my Portege (which is bare metal) for instance ... in fact, plastic laptops are sprayed on the inside with a conductive film for radio frequency shielding (and, presumably, static dissipation) so you can take a multimeter probe to the inside of a plastic cased laptop and still get (limited) conductivity!
It just occurs to me that one potential way of telling is to leave the laptop turned off overnight (assuming it was relatively cool) then feel the base in the morning ... even with a thin layer of plastic it should feel "metallic cold" whereas plastic wouldn't feel as cold ... but then again I've felt some pretty cold, dense, almsot metallic plastic before so it isn't a reliable test ...