Kers

[wolram]

Any one know how these are coupled to the engine on F1 cars?

http://www.greentechmedia.com/articles/shock-therapy-cars-to-get-electro-power-boosters-5159.html

They seem to work well for overtaking.

[mgb_phys]

Motor/generator directly to the crankshaft.
Williams were working on a pure mechanical flywheel system but it didn't go anywhere.

The jury is out on whether it does any good or is just green-washing

Some details http://www.formula1.com/news/features/2009/1/8887.html

[Kurdt]

It seemed to make a noticeable difference to Ferrari and McLaren. At least I think so. Not so much on the Renault.