Pros:
- It's fun. I've always enjoyed riding a bike.
- Good balance between freedom of movement and travel speed.
- My commute is now my cardio exercise time so I don't have to do it at home.
- I don't have to drive. I hate driving.
- Faster than public transit.

Cons
- Imapatient drivers, cyclists & pedestrians
- Clueless drivers, cyclists & pedestrians
- Riding in rain, snow & ice. I ride in the winter but I eagerly await the return of spring.
- Having to change in & out of more layers when it's cold.

Cost doesn't really factor in for me. The money I'm not spending on a transit pass or a parking pass ends up being spent on bicycle upgrades, maintenance, gear, and clothing.