www.cyclicio.us posted an interesting tidbit about Bill Nye today. (I loved his show as a kid!) Check out both the video of Bill Nye riding a bike to demonstrate the distance between the planets and the Roger Kramer article. It talks about a study that Bill Nye referenced on the show "Stuff Happens" about the possibility that cyclists harm the environment more than they help.
The idea is that since cycling can increase a person's lifespan, they may end up consuming more resources in their lifetime than they save by cycling. However, I like that the article points out that many cyclists become more aware of their impact on the environment and change their lifestyle choices as a result. This could outweigh the impact of an increased lifespan.