Lots of good info in this thread and I would like to ride the C&O some day. Does anyone have links to web-based guides to the C&O or GAP trails?

However, I would disagree vigorously with Neil B's assessment of Wash DC, which is one of my favorite places to visit. DC is one of the prettiest cities in the USA with regard to architecture, parks and monuments. There are many things you do there if visiting for a day, a weekend or a full week. Many of the nicest places to visit are also free. Also a lot of great restaurants and a fantastic transit system. The main downsides are that hotels and parking are very expensive and -- like any large city -- you do have to take precautions with regard to potential crime.