I drive 30+ miles, bike 7 - 8 (depending on route).

It takes about 15 minutes more to bike the last few miles than drive, including the time to swap. My total commute and my schedule gets me home too late to consider riding after work, plus the reduced wear and tear on my car (and me!) is worth it.

There's a website dedicated to the concept in the greater boston area, parkandpedal.org. Not updated very often, alas.