Todd,

I did it a few years ago. Trains are cheap and run regularly (at least once an hour), but my experience at the other end was a little different from David's. There was a stand to call a taxi at the Civitavecchia station, but no waiting taxis. We waited with another couple for close to 30 minutes and ended up sharing the lone cab that finally pulled up.

There were no elevators or escalators at the Civitavecchia station (at that time anyway) so we had to haul our big bags up a couple flights of stairs (which led to many harsh words about the number of shoes I had packed). So be fore-warned...