I've never owned a car. I've ridden public transit, gotten a ride, or used zipcar my entire life. I actually think owning a car would be a huge hassle - shovel it out in the winter, find parking, pay for insurance, maintenance, blah blah blah... probably because I grew up like that.
I guess I'm fortunate to live in an area (Boston) where there's pretty good transportation options. I walk 10 min then take the subway 10 min and I'm at work. I can walk to the grocery store, ride my bike to most other places, and take a bus or train to get to places that are further away. I get a zipcar if I need to go somewhere without transit access (or pick up something large from the store). Or taxi if I'm lazy or if the subway's closed for the night. I split gas with people who give me rides. Seems to work out.
If I lived somewhere else I'd maybe want to get a car though.
I remember in my transportation economics class in college, my professor saying that in most parts of the world, transit is an 'inferior good' - consumption goes down as income goes up. There are a few areas where this is not the case.