This sounds too good to be true, but it works.  It took me a while to think of negatives for this review. 

If you try and like the service share info only with your closest friends - or those who live far away from you.  You don't want them taking all the cars!! 

Customer service can be inconsistent.  But you rarely need it.  They cannot think outside the box if something goes wrong. 

Having a car in a large city is pain, what with all the parking tickets, damage to the vehicle, maintenance, gas prices, etc.  The Zipcar is not your problem.  Just respect it while you are in it - no smoking,...