From the man who brought you DW*Link, here's another one.

The spiel doesn't mention efficiency but does mention fun. Can we assume this is more for 'gravity' bikes then?

It looks a whole lot like Trek's ABP, as mentioned in the article:

From: http://www.bikerumor.com/2010/07/27/dave-weagles...

The system's official site: http://www.split-pivot.com/