I just got home from Italy a few hours ago, so this is pretty fresh.
The Roma Pass is a great value, even with its current price of 23 Euro. It's most efficient to buy it when you first arrive at the Termini Station since Tabaccherias there sell them. Then you're free to start using it, especially the transport card, on the morning of the first day you want to count as the start of your 3 day validity period.
The freedom of unlimited use of metro and bus was priceless, as was the sheer joy of bypassing the lines and just showing your pass at site entrances. I got my money's worth just visiting the Borghese Gallery and the Colosseum (10.50 and 12.00 euro entrance fees respectively.)
I had my hotel book the Borghese Gallery for the next day after my arrival, and got a choice of entrance times. I could have even had a reservation for the same day. So if you don't plan ahead for such things, know its always worth checking. You could get lucky. When I got to the gallery, I wasn't even charged the 2 Euro reservation fee.
Sonia
I too used it for my trip a few weeks ago and it was great. Though I did start using the Attractions card on a different day than the Metro card... apparently, you're supposed to begin both on the same day?
If you buy a 3-day Metro card separately, it's already 11 euros so as long as your two museums add up to at least 12 euros, you've made your money back.
I concur! I highly recommend the Roma Pass. You can get it at the main train station (tourism office) or airport. It basically gets you into two museums for free, other museums at a discount, and all buses and metros. It's the cost of two museum entrances but you get the ease of being able to hop on and off a bus or metro anytime even for just one stop. Plus they give you a good map of Rome and a book that tells you about each museum, their hours, cost, and major sights. The best part is you could call the customer service number and ask anything like "I'm trying to go from here to there - what's the best way to get there?" and they'll tell you exactly what bus/metro to take and saves you time and money of cabs when the public transportation is easy if they tell you what to take. Check out www.romapass.it. We used our Roma Pass for the Coliseum and Borghese. Use it for your first two most expensive museums so you can get the discounts on the ones after and get the most out of your Roma Pass. You can call the Borghese 0039 06 8413979 and make an appointment letting them know you'll be using the Roma Pass.
The metro part of the card and the museum part are completely separate systems and each have their own "clock" thats starts at first use. I made the mistake of using the metro part too early while my wife started hers the next day. So her bus and subway part worked one more day than mine did. And that last day just so happened to be a day we used the transportation system allot.
The Roma Pass is the greatest deal in Rome but to use it wisely, don't start it late in the afternoon on the first day cause that uses up one whole day at midnight. Start it early on a morning that you are going to see lots of stuff. Buying the card doesn't start either of the two clocks, museum or metro. Only first use starts the clocks.