Here's what I am already noticing about having four wheels full time. I drove to Trader Joe's and the bank instead of walking and they are just a block from my house. However, these two trips were tacked on to other driving excursions, one being my yoga class in Castro Valley. The car ride to yoga seemed to take as long as riding BART. Some of this time may be attributed to me getting a bit spun around looking for highway entrances.
But I am also noticing that on a bike I can more easily merge onto the road and take spontaneous shortcuts in heavy traffic. In fact, I don't even notice the traffic when I'm bike riding because I fit so nicely between the cars and the curb or in the bike lane.
I am also developing a concern that I will eat at my regular level and not burn the calories. Maybe I should use the high cost of gas as a motivator instead.