Nuvinci on an electric bike
I bought a NuVinci hub built into a wheel for just over $500. I put it on my Giant Lite electric bike.
The Giant Lite is a fairly unique design for an electric because the motor drives through the drivechain in parallel to your own pedalling input. The controller on the motor decides how much to contribute based on your cadence and the load it senses on the drivechain. There is no throttle for the motor.
The ability to tweak the gearing ratio of the NuVinci as I ride makes the electric bike even more fun. I'm able to control gearing enough that I can add in or take out the motor's contribution as I need it. With a fast cadence I can ride over the gearing and the motor reduces its contribution to zero. On hills or into a wind, I can find the exact gearing that will optimize the motor's contribution.
My battery range has improved. I haven't done a scientific measurement, but I think I'm now able to extend my useful riding range from 20 to almost 30 miles. I'm now riding 13-15 miles per day and using less than half the charge on the battery.
I've been riding this setup ever day for six weeks now - 300 miles or so. So far, no problems to report. The motor adds between 240-370 Watts to my own efforts, but there has been no slippage or noises yet.
The extra weight is less of an issue since I'm already riding a 50 lb bike and carrying all my commuting gear and work stuff. What's another 10 pounds (except when the battery dies :-) )
The initial usage experience has been very good, but it's taken a few weeks for me to truly understand how to optimize the increased gearing ratio control to both extend battery life and get maximum assistance when needed.