I think that our climate is a bigger obstacle to increased bicycle commuting than the roads are. The winters are too cold for comfortable riding, the summers too hot, and the spring and fall are too rainy. I know that I can rarely spend a full day on my chopper because of the climate, choosing instead to use it to run errands or just do recreational rides when conditions allow. (Early or late in the day for example..) Its the same reason why the roof stays on my Lotus about 90% of the time; our weather is just too extreme to be out there in the noonday sun.
We could build a million miles of bike trails, but I suspect that unless we enclose and air condition them, the only people who will use them are folks who have no other alternative.