SEA-FCO flight on Continental/Alitalia

That's a bit of a tight layover. It looks like their international flights depart out of Terminal B and the domestic (non-Express) flights are out of Terminal A. So you'll likely have a terminal change and hope that you come in on time and your luggage makes the change.

I would expect Alitalia to be strict about their weight limit. To expect otherwise could lead to some last minute adjustments (not to mention your already tight layover).

Here's a terminal map for Newark:
http://www.continental.com/web/en-US/img/travel/terminals/terminal-ewr.gif

I don't know if this will make you feel better, but I'll try! It's a trade-off, for sure. If you research and carefully plan and buy your tickets far in advance (I usually do that, too), you can be "hit" with these sort of unexpected time changes. On the other hand, if you wait until closer to the departure date, fares may be a lot higher and better connections sold out anyway! So don't be hard on yourself! I am facing a similar situation in reverse, from Europe. I have decided to just assume I won't make the connection and be very, very happy if I do! I hate to fly anyway and look at the whole experience as just the means to an amazing end. If the ticket is booked altogether, as yours is, the airlines will be responsible for getting you to your destination. Eventually! Just make sure to take a change of clothes, etc, if you check your bag. (It might be worth it to pack within the Alitalia limit so you can run with your bag if you arrive on time in Newark.)