This trail ride sounds great! Who knew you could ride from Washington DC to Pittsburgh (or the other way around)? The Great Allegheny Passage and the C&O Canal connect and give you 300+ miles of smooth (ish!) sailing. You can rough it by camping or stay in motels/hotels/hostels/B&Bs. There are all sorts of options, from day trips to 11 days.
Lots of people have sample itineraries and FAQs about the trip. Here are some that I found helpful: http://www.bikewashington.org/canal/, http://shaw-weil.com/linkup/index.htm
(plus the GAP logo is great!)