Firstly, I'd encourage you to take a look at the US CLT thread. I know there's some customs/immigration questions there, and I may eventually merge your thread into it:

http://www.flyertalk.com/forum/us-ai...e-airport.html

Secondly, as someone else said, if a flight from Europe is delayed, the whole transfer could turn into an hour + experience. I've done it twice through CLT, once from FCO and once from FRA, the FCO flight arrived around the same time as 1-2 others, and it was near chaos. The FRA flight wasn't nearly as bad.
Keep in mind that you'll need to re-clear security after that, which could also take 30 min or so.