Yes, a ZipcCar membership allows you to reserve and drive anywhere zipcar operates. I don' believe that hourly rates are uniform across the board, and there may be variations in the insurance deductable if you don't buy the waiver.

This is one of the nice features. I can take the train to another city, use a ZipCar for a while there, and train home. I only wish ZipCar was more like bikeshare where I could pick up in one place and leave in another. I'd even be willing to pay extra for alternate drop off but it's not offered.

I don't know what part of Bgreen's use of a ZipCar didn't match how I described ZipCar, I thought it matched perfectly. Note that though he kept the cars for a few days, he picked up and dropped off in the same location in each city.

However, if you're actually interested, ZipCar has a site, and offers explanations of the various ways to use their program.