i'd have to agree with joe and jaydee.
i think there's a lot of variables here that just can't be known.
the improvements in processor construction will likely reduce the heat output of the device. if i recall, the newer, much faster xp processors put out less heat than older models? i think this will continue to improve, and i doubt the increases will be as dramatic as some may think.
also, there will most likely be vast improvements in aircooling technology, as was pointed out. i mean, looking at the air cooling device i use now, and comparing it to the aircooling device i commonly used a few years back where i used to work, are QUITE different.
materials are another big part of that equation. not that long ago pretty much everything was aluminum for air cooling, but now that has advanced so a good margin is now using some part of copper to increase efficiency.
not only that, but you'll see design enhancement in the physical design of the devices as well that will improve performance dramatically as well, just as they have in the past.
and, i think as well the use of heatpipes will increase and become more efficient just as standard aircooling, and be an increasingly viable option. they will progress with everything else.
just my .02
