No, I've had terrible experiences with UA, especially since March 2012, and I hate them as much as the next guy. I try to avoid them noawadays. But if your flights are on a single PNR and you misconnect owing to their own operational problems, they will rebook you, not attack or ignore you. You might have to stand in a line and endure rude personnel but you will get on your way. The OP is worried enough about his trip that we shouldn't be creating new unnecessary fears.