After those guys demonstrated that biking across LA was faster than taking a plane, I thought bike vs. car would be a no brainer.
For me, driving is about 10-15 minutes faster, depending on traffic. If I leave work at about 5:15, the first street away from my office complex is usually backed up close to half a mile with cars waiting to get through a single traffic light, while I cruise past them on the bike, but within a mile roads open up significantly and a car from the back of the line going the same way I am would probably pass me about the time I'm halfway home. I'm OK with that because I didn't spend the first 15 minutes of my commute wishing I was doing something else. I see the way they look at me while they're stuck at that red light, and I know that they're jealous -- not jealous enough to give up their precious car, but still jealous.