I live in DC and cannot recommend Zipcar highly enough. I sold my car before moving here from California, and usually walk or use the excellent Metro system to get around. For those trips to Ikea or other out-of-the-way places, Zipcar works great. The cars have always been there for me as advertised. There are sometimes obvious stains on the seats, but no abject filth or anything like that. In fact, if there's damage or anything wrong with the car, you're supposed to call Zipcar to report it, and they'll direct you to another car if the problem is bad enough.

I've also used Zipcar for a four-day road trip over Christmas, and it turned out to be cheaper than renting since it was during the peak period, gas and insurance were included, and I'm under 25 and thus would've been subject to the underage surcharge with a rental.

Zipcar's insurance coverage dramatically improved a few months ago; instead of state-mandated minimums, Zipsters now have $300,000 of comprehensive insurance with a $500 deductible for third-party or vehicle damage.

Another great bonus is that Zipcar usage earns Amtrak Guest Rewards points!

Also, your Zipcar membership is good in all other Zipcar cities as well. ^