You may never meet the people you impact. At work, my behavior has affected one guy. He bought a bike and uses it to commute a mile and a half.

However, I once encountered some guy on the road who said "You are my inspiration! When I saw you out every day no matter what, I knew I had to do it!". This dude commutes more than 15 miles each way, but I rarely see him because we work at different times. He started serious commuting in the winter of 2004, and I met him in spring 2005. I told him that once you've been out an entire winter, it gets pretty easy.

I think trying to actually convince people may even turn them off. Reminds me of one of the mottos I've always lived by -- "Beware of crusaders...."