I wouldn't play the 'smoke in the cabin' angle quoite so hard in your letter to UA - I think I'd rather go back to the gate than take off in that situation, even with a lack of information! And not meaning to be picky for the sake of it, bags do get wet when it's raining - they have to be unloaded from the aircraft and if the rains coming down, they're going to get wet - waterproof luggage is a good way to go. Further, UA may be able to put at least one of the delays down to that same rain.

All that said, it sounds like you had a tough trip and it is horrible when these things compound. Good luck - it will be interesting to see if UAs changing attitude to customer service is based at all on customer perception.