Without knowing how common these problems are, it's really hard to say how much this sort of stuff affects the average user. Reading through the list of problems, I had a momentary freaked out feeling that made me think I'd never use the service, but the author still loves zipcar, which makes me think these problems aren't all that common. Or, not common enough to outweigh the benefits of using the service.

Still, it's nice to hear a fan of a service talking about problems with it. It's very considerate to mention the problems with something whenever you recommend it.