I'm using a bionx right now, but, of course, I still want something lighter and faster.

The hub motors limit you on the flats and downhills. The electromagnetic resisitance effects are stronger at the higher speeds. I've tried hand cranking a bionx wheel vs a regular wheel which the bike elevated and I had a hard time making the bionx wheel go faster than 25mph.

Because the bionx wheel is in the back, you can feel the imbalance between the front and rear (esp when I even had the batter on the rear rack once).

I believe a BB drive will allow you to go faster on the flats at the same power output. And for the downhills, not only will you go faster because of the absence of any electromagnetic resistance (there was a name for this but I can't remember it now), but you will really get the benefit of coasting down with a heavier bicycle.

So I'm just waiting for someone to build the perfect BB drive system. The stuff at elationebikes look great. If they have a nice controller like Bionx, I might consider it for my next e-bike.