A query

Harold the Consumptive Oldsmobile of Doom has had a long-running case of the creeping fail that has progressed to the point where fixing all the things that are wrong with it may no longer be worth the cost. To that end, I'm looking to take the thing off the road sometime after the end of the current temp assignment, i.e. next month. However, since the idea of buying a car at a time when I don't have a permanent job scares the living pudding out of me, I'm wondering if the Zipcar theory might be the way to go. Does anyone here have any experience with Zipcar, especially Boston-specific experience? Pros / cons / recommendations / suggestions?