The reason that heatpipes work so much better is that basically they operate like mini phase change coolers. Instead of using a motor and compressor to facilitate phase changes, they alow it to do it at its own pace. The fan & fins around the heatpipes work just like the compressor on a phase change unit, only way slower.
Have you ever noticed that in some of the heat pipe coolers they have specific ways to mount them, especially if the pipes are at weird angles. This is because the gas has to to be able to move... up... and then come back down after it changes back into a liquid. otherwise they don't really work all that well. The ones that don't have a specific mounting postition use a "wick" on the inside to move the liquid along via capillary action.
The phase change is way more efficient than just moving the heat somehere else (IE, a solid copper tube) Its not just the thermal conductivity of the refridgerant in the pipes, the simple fact that its changing phases is what makes it so good. Changing phases takes alot of energy, thats what eats up all the extra heat.
anyway, other than the fact that silver costs WAY more than copper, the % differance between the two is pretty small... I really doubt that you'd notice a huge change in temperature. Although it would be cool to say you have a silver waterblock.
EDIT: so as it turns out, college chem actually DOES apply to everyday life...Edited by logan - 6/20/08 at 4:43pm