Engine cams are actually quite efficient. I know the springs are pretty hefty, but whenever you push one valve open against a spring, there is usually another valve closing with it's spring 'helping'. All the engine is really pushing against is friction, Which isn't alot when you consider they all run in a slippy bath of oil.
In the Koenigsegg the valves are all independantly pushing against springs, and using pnuematics. That's got to draw some power!!! There must also be a compressor somewhere?! So the engine combustion may be more efficient, but the system around it can't be? Maybe I'm wrong, perhaps it can do 50-60mpg like my car with normal cams?!
The biggest advantage is probably the variable timing options, although I don't think that is new technology either?!
All mind blowingly cool stuff, anyway. Although I'm not sure the technology will ever translate to modern cars.