I bike on a road bike, but then I have:
a 16 mile each way trip on a well paved and traveled bike route.
rain ~10-15 days a year.
a walk in closet that I can lose my bike in at work.
no real need to transport anything but myself to and from work.
pretty open hours as to when I start/stop work.
It's amazing that there's not more people biking to work... they just don't feel like it I guess.