We do have a car. . .but use public transportation frequently. We did not own a car while we lived here until I was pg w/#3 so I was very pg and toting a 2yo, and 4yo. It is substantially cheaper to use public transportation and often it can be quicker bc you're not subject to traffic delays--at least on the subway. Strollers, IMO are a pain in the rear end in the city so that's how I ended up doing so much of the baby wearing thing--even w/the twins. You can take strollers on the subway but on the buses you'd have to fold your stroller, carry the baby (

or babies) and your 'stuff'. . .just easier to carry your little person or take something else.
Our van is slowly heading towards its sting in the junkyard. It has been good but we've driven it into the ground. So we were recently contemplating giving it up and using zipcar.