My motivation is my weight, I really want to loose weight and this kills that bird as well as a bunch of other birds. I am motivated not only by weight loss but also seeing my gas bills drop. Another big one for me is that I seem to be a lot more mellow when I commute then when I drive, I seem to get a lot less pissed off at the people around me since I am so focused on not crashing and pushing myself to go faster.