The Metro is a fantastic way to get around. Instead of driving through and maneuvering the streets of Washington, you can take the train from place to place.
By getting around this way, you can save some serious cash by staying outside of the city, and still be close to the action. Parking is affordable (a couple of dollars for the day), train fare is affordable.
Make sure to pick up one of the pocket sized maps of the system. It will help you greatly in getting around, especially if you are new to the system.
The trains were clean. They are like most mass transportation systems. When you get out though, be warned that the escalators are fairly steep. If you are a bit skiddish of heights don't look behind you, just straight up. They are indeed safe, but the incline is a bit steep.
Overall, a great way to get around the Beltway without driving, and to see the sights.