Amtrak makes it easy to travel, especially if you are lucky enough to live on the East Coast. I can't personally speak for any other area of the country, but out here it's straightforward and convenient. Just get yourself to a station, use a user-friendly kiosk to print your tickets, and hop on your train. It's definitely not as cheap as riding the bus (for instance, there are many "Chinatown" buses that run between DC and NYC that run you $20-$50 a trip), but you get the luxuries of no traffic, comfortable seats, lots of space, nice views, Wi-Fi, and a food car. Sounds pretty good to me.
The main Northeast Regional route runs between DC and Boston. We stopped in Baltimore, Wilmington, Philadelphia, Trenton, Metropark, Newark Airport, Newark, and New York City, while I was on it. One note about traveling this route is that there are a lot of "Penn Stations" - Baltimore, Newark, and New York all have them.