Since the topic of the Italian trains and on-line reservations seems to always pop up, I thought I'd just let you know that I booked my "ES" trains today for Florence to Bologna, and Parma to Venice. It was very easy to do (easy registration, which I got my password within minutes).
The one interesting thing I noticed is that for the Florence-Bologna ride I was able to choose the tickless way, where as the other ride I had only 2 choices, so I chose the "self-service machine ticket collection," which should be pretty easy to do.
The ticketless option is available only on top trains, those whose conductors have a small wireless computer to retrieve the ticket data from a central server and print it.
the ticket machines are extremely easy to use, and you can choose to do it in english if you're italian isnt great. just makes sure to still get to the station a bit early as there can be lines. all you need to get the tickets is the name of the trenitalia account, and the PNR number (I think it was PNR... or some abbriviation like that anyways).