Looking at Apple's specs, the operating ambient temperature range for these machines is 10°C to 35°C.
Needless to say, I routinely run my laptops on the high end of these temps, if not higher, which is a good enough reason to be concerned that those figures may not just be a matter of CYA on Apple's part.
Add to that the double issue of battery life and dust buildup inside the machine, both of which are tied to how often and how hard the two fans at the rear of the MacBook have to blow on the CPU/GPU heatpipes' heat exchangers, and it becomes obvious that anything which can be done to improve the cooling of this laptop by other means is a GoodThing™.
[Speaking of which, I'm not entirely sure how much of the air intake is done from the rear grille and how much is dependent on semi-improvised various holes such as around the keyboard, etc.]
Since I want to keep the drilling through the MacBook Pro chassis to a minimum of roughly zero (and it's not like there's much room to spare inside the box anyway), the back of the display casing seems like the best place to hook up some external cooling apparatus.
Yet before I even begin to worry about where the heck 'plate' type heatpipes can be procured, or how to build a small thermosyphon, I'll have to figure out the first and so very weak link in my thermal chain, ie: how to extract the heat from the 'cold end' of the factory heatpipes, and bring it to the 'hot end' of a back-of-the-display thermal circuit ?
The wiggle room between the internal heat pipe and the unibody shell is about 3 millimeters at best, and right next to the rear grille, so I figure a sheet of copper attached with clips and connected with thermal paste to the 'cold end' of the factory heatpipes can get me out of the chassis without sigificant adverse effects on the factory cooling system.
…yet from there I still need to work my way around the bottom of the display (which rests inconveniently below the topside plane of the main chassis) to reach the 'hot end' of the external heat dissipation circuit.
And no, hard plumbing is not an option, the display must still be able to open, adjust and close with the external cooling system mounted on, so the thermal bridge better be flexible.
[See here for an in-depth look at the innards of the 17" MacBook Pro Unibody.]