Personally, I have never had a negative experience with a Zipcar. I had an Audi A3 breakdown in SF on the way to Startup School, I told them I had an appointment. They instantly called me a cab, booked me a new Audi A3 in the FiDi and refunded my entire reservation + $75 in driving credit. Also, since I was under 21 at the time, they had to change the reservation to my passengers account since I couldn't rent cars outside UC. He also was not charged for the reservation and got $25 in credit.

The cars are always clean and I have never had a low fuel situation. Now, I rent cars in the Downtown Oakland area so I can't say the same for SF but thats just me. Oakland/Berkeley does have the weekend availability problem but if I know I am going somewhere on the weekend I can book as late as Friday night and still get a car I want.

The cost. I pay as low as $7 an hour for a Mazda 3, $9 an hour for an Audi A3, Mini, VW Golf. I have a small discount via FoundersCard however. Still though, those prices are pretty great to rent a car, especially since Zipcar covers gas, maintenance and insurance.

Insurance. If you do not have a waiver, you pay the first $750 of an accident, Zipcar pays the rest. If you have a waiver ($10 a month), you do not pay anything. Also, it counts as real car insurance so when you do buy a car and need auto insurance, you can say you have had continuing coverage. http://www.zipcar.com/how/faqs/what-damage-fee