I flew HUB1-HUB2-HUB3 yesterday. Delayed from HUB1-2 due to the fact that it takes UA 55 minutes to load a 738 for some reason, ran between terminals to get to my HUB2-3 flight to find its gone on an MX delay but the app hasn't updated Fix the MX issue after an hour, we all board and then sit and wait for paperwork which the Captain explains isn't coming because the maintenance computer network "is down". Plane is taken out of service, we deplane and they begin the search for a replacement, I'm now 3 hours delayed and slightly fed up so I call the GS line, wait 20 minutes and am told by an agent that she cant re-book me on one of the other flights between HUB2-3 because they are all sold out and that only applies if the flight is canceled. I asked about the guarantee and she said that only applies if seats are available. Got home 6 hours late, never saw a GS agent at the gate, never had a call and the only thing the Club agent said was "good luck finding a seat back there". Its pretty sad at this point.