I just took the Amtrak from Southern California to Seattle.

Pros:

- space! wide seats and leg room are awesome (I'm 6'5" so this is everything)

- Freedom to move around and explore. Lounge car, dining car, snack bar

- Spectacular views

- Train stations are much more pleasant than airports

- Opportunity to meet people from all over the place. On a plane everyone is going from A->B, people on the train could be starting/ending anywhere along the route, including small towns you've never heard of.

Cons:

- 32 hours of travel

- Pay an extra ~$500 to get a bed, or sleep in your seat

Overall I have no regrets but I'll probably not do this again until I'm retired or extremely bored.