I've taken the Metroliner (DC-NY) a couple of times (this was a few years ago). It's not too bad, especially when the flight you were supposed to be on has been canceled!
Like Dee said, it's a good idea to travel light.
There are power outlets in each row of the car, so you can plug in your laptop, recharge your cell phone, etc.
You can buy food on board, but it's expensive and not very good. Pack your own if you can manage to do so.
Have fun!
