There is a company currently operating in DC, Philly and Boston called zipcar that offers cars strategically positioned around a city for rental by the hour (or day, but at insane day rate prices). Apparently the market is for urban city dwellers who don't have a car but occasionally need one. The fleet consists of a lot of Golfs and Beetles and some other cars including in the DC area at least several Minis -- and one Miata! (Now I know where to go to get my fix!)

The website is zipcar.com. You sign up and they send you a car, you reserve the car for a time period and use your card to enable access and off you go. One of my friends uses the service frequently. I picked up a card too. Want to try out a straight Cooper and some warm Indian Summer day -- that Miata up in Adams Morgan.