We recently had a very stressful time at Chicago airport where we had to change for a flight onward to San francisco. Although there was over a 2 hour gap between landing and getting our onward flight the lines going through the baggage scan were horrendous and were like the really bad lines you get at a popular ride at Disney. We tried to tell the people "marshalling" the lines that we had an ongoing flight in a few minutes but just got attitude and kissing of teeth for our pains. We were lucky that the flight ended up being delayed so we still managed to get it. Apparently normally the flights will still go even if your luggage is on them but you are not! Really secure huh?

Just be aware if you are booking flights with onward flights as I've heard the warnings about immigration being bad but didn't realise the baggage scans/checks would be so disorganised. I'd say leave at least 3 hours between flights.