Pictures of the Porsche 918 Spyder and now the race version, Porsche 918 RSR, with the flywheel accumulator are all over the internet.
Take a look here for detailed info and lots of pics:  http://www.unfinishedman.com/porsche-918-rsr-hybrid-race-car
Porsche knows their stuff. This looks so much better than the old Carrera GT.  562 hp 10,300 rpm V8 + 2 x 102 hp electric motors at the front wheels.  

Of all the pictures I found this to be the coolest.  
That "flywheel battery" thingy looks like some kind of EMP/Nuclear-bomb ready to explode.  Imagine going trough tech inspection on a local track day with this device strapped to the floor of the Miata. "Relax, it's just a heavy fly wheel spinning at a trillion RPM's."

Porsche does the right thing. Keep the fun, nasty, noisy old combustion engine for doing the real work and complement with electric power for boring things like cruising, parking, city driving etc.