my northbridge is cooled by heatpipes, seems a good idea in theory, they must be good as most high end coolers use them now.

im using an all copper zalman flower atm on my Intel Duo which is overclocked from 1.8 to 3.2 and it doesnt go above 35degrees and is near silent

http://www.tekheads.co.uk/s/product?product=603912

Im looking at something of this ilk for my next build as I want to try and go silent.

I think in order for the cooler to remain passive you have to have a good airflow through your case already, or no hotspots to gather around the CPU.

ive got Heatpipes in my 6000+ reference cooler, as do both of my notebooks.  They increase heat dissipation without the need for masses of surface area.  The theory also says that they take the heat away from the CPU faster.