I was curious about regen shocks when the article came up a while ago. I was more interested when Mazda developed an reclaiming system for their new vehicles. It got me thinking about similar devices I had that cost near nothing.
I used to have a flashlight that you could shake to power, it had a large capacitor to store power and was so incredibly simple. The problem was that it was made out of cheap plastic and thinner than hair wire.
I was thinking that a small neodymium magnet (something like a bucky ball or bulk set of little cubes) in a container with a spring at either end of the tube might be a good idea. The spring would hopefully keep it from eventually smashing the container apart, but also keep it quieter and help keep it in motion. It could possibly even be a rolling design, doesn't have to bounce up and down.
I'm not sure where best to safely mount such a thing. Maybe a row in the engine bay. Maybe they could be kept safely on the wheel struts. I wonder if it would be worth the effort.
Shake-A-Can Generator : Shake
What other 'shake' designs come to mind? Calculating the size and shape is one thing but everyone's roads are different.