I really can't emphasize exactly how true this is. Do not be surprised if your bags come out on the belt at FCO more than an hour after your flight lands!

My recommendation? Make sure you have some change in Euro coins before you get on the plane, save some reading material, and get a comfortable seat. There are decent (by American standards, but not by Italian standards) self-serve espresso machines dotted around the baggage claim area; if life gets too hard to bear you can always pick yourself up with some caffeine