UA didn't charge me a fee for a flight change (I had 5 hours between two flights, from LAX to ORD)...When I noticed that, I called them and they said my flight was the only still available. The next day they sent me a message regarding a change though, so I called and they put me in another flight, 1 hour and a half earlier, no charge. This is part of the same roundtrip ticket, I was lucky and happy about it, but didn't get the same result when asking about these particular two flights.

And thanks for your answer on checked bags. I hear there is a lot of walking to do from one terminal to another as well, hopefully there is a nice cafeteria and wifi to get online while waiting, at least I can read something, or visit these forums or write an email or make a phone call.