Bike Anti-Porn - When Things Go Wrong

NuVinci geared hub, costs about $350-$450, weighs 4.1 kg (!)...
http://www.fallbrooktech.com/nuvinci.asp
http://www.bikeman.com/HU0103.htm

so although it's really cool technology, it's way too heavy.

Ball bearings? Traditionally used to minimise friction, hubs, BBs etc...
What would the efficiency of the power transfer be here, compared to a standard chain?

Cool technology? What's the efficiency?