We just got back from our Italy vacation and had the opportunity to use the high speed trains. They were great. We used the Rome train station and wanted to just give a few tips/info.
In doing research, we found many comments about the Rome station, a lot of them negative. It is a modern station with 24 train platforms. As you can imagine, it can be very busy with people getting on and off the trains. The station is clean and has shops, restaurants, pharmacy, quick-eat places. It is short on seating however, so if you arrive early, you might have to sit on your bag!
As many have posted, it is best to use the ticket kiosks to get your ticket, if you don't have one. They are touch screen, multi-language, easy to use. One tip. When you are paying for your tickets at the kiosk with your credit card, don't quickly stick the card in and pull it out (like we do for most transactions). The machine will not accept it. When it is time to pay, insert your card and leave it in the slot until you get the transaction completed message, about 5 seconds. Then remove the card.
If you want to use the ticket counter instead, you will have to first pull a number before getting in line (Think DMV). You may have a long wait to see an agent!
One note about the local "helpers" at the station. These are individuals who want to help you with the kiosk or lead you to the train or put your bags in the train car. They do not work for the station, but are looking for a tip from you. That's not so bad, but the problem comes from the tip they want. One helper helped a couple place one suitcase from the platform onto the train car. They tipped him a euro, but that was not enough. The helper followed them onto the car, to their seat, and asked for more money. When they gave another euro, the helper asked for more. It was not threatening, just rude, pushy and embarrassing. Best thing to do: just ignore them, don't let them touch your bag and walk away. Just put your own bag into the train car and then into the overhead rack. If you do get stuck with one that will not leave, tell him to leave or you will get off the get the police (they are in the station). They will leave.
I am sure in the midst of the crowds, there is a pickpocket or two. But we had our money secured in a money belt and kept our bags close. No problems at all.
Finally, to use the restroom, we had to pay the attendant $0.70 euro....or at least the person told me he was the attendant!