Volvo is becoming interesting again. 4 cylinder from 0 to 100 km/h in 5.5 seconds and at the same time saving fuel? This is nothing but amazing.
I'm also wondering if this would be more logical inside rear drive car? Or this is what they are doing here? In general Volvo produces front drive cars.

The idea of a flywheel for storing kinetic energy on the rear axel is an interesting new departure from Volvo which they reckon reduces fuel consumption by 25%. Great for urban driving where there's lots of stopping and starting or for undulating terrain making this the ideal car for San Francisco and Monaghan

Congratulations Volvo - re using energy has got to be good'

I suppose that this concept is another function that GPS can be adapted to. Knowing when the vehicle is going to reach its destination, the GPS could ensure that all the stored energy is used up beforehand so that it does not go to waste while the car is parked.

I think it could be used in addition to the regenerative breaks on hybrids and electric cars. The flywheel could be attached to a generator and produce electricity when needed and/or charge the batteries?

No magic here but nice implementation. Since it was tested in a 4-cylinder car how about comparing it to a 4 cylinder car rather than a six i.e., what are the fuel savings then? Is it approximately equivalent to a turbo without the fuel losses associated with higher RPM and fully depressed accelerator? What about the possibility of pairing it with a diesel where RPM are lower by design? Since it is reliant on recovered stopping forces what is the ratio of benefit to weight of vehicle in a standard driving cycle? Is there an optimal braking pressure, such as mashing the brakes and letting the ABS take over, or will feathering the brakes spin the KERS up to full speed? If the vehicle is equipped with handling assistance, will single wheel braking also activate the flywheel?

I agree with BigWarpGuy, that research and development of an all electric car using this flywheel system should be fast tracked. An all electric version might pose quite a challenge to Volvo, the company being accustomed to producing relatively heavy cars these days. Now it will have to get both light and super safe.
Get an electric version out on the street immediately, refine it and offer generation 2.

Seems like a metal flywheel would be less expensive as it is the mass that creates the flywheels stored energy. Must be a good reason for CF. I felt the flywheel would also be a good application for the stop start systems in use today as it could be energized in a similar way and then coupled to restart and aid in initial acceleration.

An energy recovery system that can actually pay for itself and wont loose capacity as it ages. Very Good!
Why would anyone think that putting a flywheel energy recovery system on a car that already has an energy recovery system is a good idea? Especially when the the electric car is already too expensive.

Slowburn, I think the issue is more complexity, than cost, as KERS is able to recover a greater percent of braking losses (because of the ability to store more energy in a smaller time frame than chemical battery storage)
The carry on from this is that the range is increased by one of these units, you no longer need some of the chemical batteries capacity, therefore you are able to reduce the cost and weight of the batteries.
Part of the problem with the capital cost of electric cars is the batteries are often an upfront cost, when they probably should be an ongoing cost, like fuel and engine servicing in a conventional car.
The Renault Zoe in the UK is using the strategy of selling you the car, but leasing you the batteries, creating a cost structure that makes much more sense when you try to compare equivalent conventional car costs.