I'm from Kansas and I rode from Cumberland to DC in June 2006. I flew to Alexandria, rented a car for 1 day one way to Cumberland, DC (Hertz), and rented a mountain bike in Alexandria for a week. I left my large suitcase that had my panniers in it at the Holiday Inn in Alexandria where I would stay for a few days when I returned from the bike tour. The hotel also had free shuttles to the airport/Metro station. I drove to Cumberland and stayed in a motel in Frostburg (5 miles away and much cheaper). The next morning I left the car at the gas station/Hertz place and started on the C&O that was only 2 blocks away.
I stayed in motels and B&Bs in Little Orleans, Hancock, Shepherdstown, Leesburg, Alexandria. The longest day was about 44 miles. The trail can get muddy after a rain. You can get some great info on bikewashington.org.
When I returned to DC, I rode from Alexandria to Mt. Vernon on the Mt. Vernon trail--seemed like it was downhill both ways, riding paved after 5 days on the C&O.