They are a good idea that does not really work. They have had at least 2 incarnations in the past and have been weighed in the balance and found wanting.
http://go.bikeforums.net/?id=42X1295...2Fbiopace.html
I used to think and Sheldon and I were the only folks who appreciated Biopace rings... they have their place and are not for everyone but the science is sound.