imo.
you'll have two problems with a heatpipe waterblock.
first, you're adding another layer to the heat transfer,
second, there's optimal temperature points to heatpipe operations.
managing both is not as easy as making a plastic tube around it.
edit:
what i mean is that a heatpipe depends on larger temp differences,
means is that if you cool it too well, it wont be as efficient, as temp differences between
the base and the fins will be reduced considerably.
well, at least that my take on heatpipes.
edit 2:
remember this?
http://forums.procooling.com/vbb/sho...6&postcount=55