Chinatown Busses run from many cities. I've seen ones that go as far South as Washington, D.C. and as far North as Boston. Some busses go to other, more out of the way locations as well. Many Chinatown Busses focus on New York City's Chinatown. Chinatown Busses are cheap, relatively quick, and fairly comfortable. Despite the previous w/u, many Chinatown Bus companies now use proper busses with fabric covered seats, air conditioning, and audio/video systems, showing bootleg movies.
To make the most out of your Chinatown Bus experience, make sure you get there early. If your bus has televisions, the best spot to sit is one row in front of the TV, so that the light doesn't keep you awake. Bring a portable music player of some sort, as well. Pack light.
The people running Chinatown Busses do not, ever, speak good English, so make sure you have your tickets prepared in advance. If you have any problems, be prepared for a screaming match. Fortunately, they know the customer is always right, and will relent if they are in the wrong.
Do not use the bathroom on the bus.
Relax, and enjoy your bus ride.