We used Streetcar for a few years and LOVED it! We have something like 6 cars within ten minutes' walk from us and there was always at least one available when we needed it. We'd really only use it to go big box store shopping, so it was really useful for Costco and IKEA runs.
The only thing you have to be careful about is to always be REALLY anal-retentive every single time you get in the car and do a thorough check over to look for any tiny scratches or dents and report them using the in-car system before you move the car, because if you don't report it and the next person does, you'll get the blame for it! But as long as you always do that, you'll be fine. And the customer service people are awesome, they're there all the time, even Christmas Day.
The only reason we stopped streetcar at all was when we were forced to buy a car immediately after my transplant because of germ reasons (you don't know if the person who used the streetcar before you had a cold or something). We love our car now, but I still have a warm place in my heart for Streetcar.
(And CB, I just unsubscribed from Groupon because I'm SO annoyed with the 95% crappy spa deals I don't care about. They should call it "Spa-on"!)