This isn't a first hand account - so please take this with a grain of salt. I was also considering going by autotrain for our next trip and then my in-laws took the autotrain and they were really unhappy with it.
First, they sat in coach which most people also do since it turns out to be cheaper to fly if you get the more expensive private sleeper "cabin". (I know that I would probably enjoy my own compartment, but it sort of defeats the purpose of going by train if I can fly cheaper and faster.) They said the seats were comfortable, but not great for sleeping. Also, the coach area is noisier since people are constantly getting up, kids are crying, etc. So, they found it hard to sleep.
Second, they had some issue with the food car. I guess that there aren't "seatings" and there are people that stay there to have coffee, etc., and so it is not very easy to find a seat. We always travel with my parents and it sounds like trying to find a seating for 7 might be difficult.
Third, they say it took a long time to get there car from the train when they arrived. Now, my father-in-law has a gift for impatience, so I don't really count this one. (He's the sort of guy that is waiving down the waitress 30 seconds after he sits down at a restaurant to make sure she waits on him in a hurry.) What may seem like a reasonable wait to most was something that he complained about.
I still am considering this since I like new experiences, but after their trip, I find that I am really weighing the pros and cons.
(Anybody whose had a first hand experience in this, please let me know if the IL's were wrong. I still think it is neat to travel by train!)