Boarding is heaven compared to flying. No security theater, no ridiculous parking issues. I used to ride from Rhode Island to DC, and I could literally arrive 10 minutes before my departure time, grab my bags, lock my car, walk 100 feet to the platform, and still make the train. The trip took most of the day, but now that cell service is no longer an issue, it's possible to spend the entire ride relaxing or getting work done.
And I can't believe no one has talked about how much better the seating is than any other form of long distance travel in the US.
I recently traveled from BOS<->NYC for business. I left my office an hour before scheduled departure and walked 30 minutes to Penn Station. A slightly different experience than getting to Newark/La Guardia/JFK. As a bonus, I was returning on short notice, so I was able to easily change to an earlier train 10 minutes before it departed, with no extra fee.
At the end of the return trip, I overheard a group of four other travelers saying that they got so much work done, they should just ride the train back and forth every day.
Seat and ride comfort are totally different as well. To me, it's well worth trading in some time for a much better travel experience. I've had a year where I logged close to 50k air miles in coach and over 10k train miles in coach, so I've seen the good and bad of both modes of travel (on and off the NEC for the trains).
For the long distance trains, I consider the time it takes to travel one of the benefits. In today's highly connected, highly active world, I find having 24 hours to simply look out the window and be alone with my thoughts to be incredibly rejuvenating.
And I can't believe no one has talked about how much better the seating is than any other form of long distance travel in the US.