I have a 2006 Macbook Pro, and it used to run very hot until I had the motherboard replaced last year. Now it is just lukewarm all of the time, thanks to the heat conduction properties of metal. Anyway, I don't think it's hot because of the materials used in the chassis, I think it's hot because the components they put in it put out too much heat and Apple's process for applying internal heat-dissipation components is flawed.
While I don't agree that the Unibody Macbook (Pros) are designed to use the entire "brick" construction as a heat sink (it's a fairly coincidental side effect that it dissipates heat), it's safe to say that there are dangers involved with insulating all of your heat-producing components in a very closed plastic housing as well.
FX is right about aluminum being soft, but from a business and design standpoint it's not that bad for several reasons; mainly it's cheap, lightweight, and lends itself well to both machining and anodization (which also makes it harder). Aluminum as a "pro feature" is just marketing.
While I don't agree that the Unibody Macbook (Pros) are designed to use the entire "brick" construction as a heat sink (it's a fairly coincidental side effect that it dissipates heat), it's safe to say that there are dangers involved with insulating all of your heat-producing components in a very closed plastic housing as well.
FX is right about aluminum being soft, but from a business and design standpoint it's not that bad for several reasons; mainly it's cheap, lightweight, and lends itself well to both machining and anodization (which also makes it harder). Aluminum as a "pro feature" is just marketing.