In my case, it helps that I enjoy riding a bike much more than taking the Metro, and even more than driving to work. Thus, commuting by bike doesn't feel like a chore or exercise routine at all.

When I first started, I read about various complaints/horror stories about bad behavior from other cyclists, motorists, bus drivers, etc. but they don't bother me as much as I thought they would - one exception being the bus that came up behind me fast and blaring its horn repeatedly. Even counting that last experience, I still much prefer commute by bike over the other two modes of transportation.