I am six years late to this party, but as a rider with about 120,000 miles of Biopace experience, I feel compelled to chime in. I started using Biopace chainrings in 1984. Having endured years of debilitating knee pain, I read Shimano's purported user testimonials from riders who found Biopace to be a miracle cure. My knees recovered to the point where I now ride over 5000 miles per year without pain. Was Biopace the reason, or even part of the reason? I will never know. In recent years, I have ridden increasing numbers of miles on circular chainrings, and a few weeks ago I replaced all my Biopace rings with round. The main reason I did this is to stop the scorn from riders who are sure that Biopace is inferior, or nerdy, or whatever. Those who claim that Biopace rings are incompatible with high-cadence spinning are mistaken. I started spinning mine before that urban legend spread, and I never had any problem maintaining a smooth pedal stroke.