Not sure Russ where did you find 99.3% figure and whether its meant for entire system or heatpipe efficiency alone. Being totally passive device its efficiency can't be very low. I guess the 0.7% loss is due to mechanical movement inside heatpipe. Whether its very efficient for heat transfer is another issue. But it doesn't hurt.
Heatpipe as such does work, and is gaining interest in PC's, due to its totally silent operation. Although its not as efficient in heat removal as rude heatsink and fan, it definitely has its advantages.
Sure its not miraculous, so don't get caught in some marketing twists. It helps to move heat from hotspot to where its easier to get rid of it without forced energy usage.
Its surely quite far from application you're interested in, but in case you've not seen it, here are few applications of heatpipe for PCs in reviews:
I find that interesting.