In 2014 (and late 2013) I have had a spate of bad luck with operations. Some above talk about statistical averages, etc. That's fine. Life Happens. But in 14 years of flying 1K, I never had as many issues as I do now, and trust me, I fly a lot less on UA now. In fact, I've got a whopping 8 segments this year.
So yesterday, I was supposed to fly the 787 from DEN-IAH, but with the impending snow I decided to SDC to the next earlier flight. Not only was I upgraded on the A320 (something that I wasn't going to get on the 787, with all those BF seats) but we left relatively on time, with only a small ATC delay and then had to deice. We arrived IAH 1 hour late. Meanwhile, the 787 had a creeping/rolling delay and eventually they subbed a 739 on the trip with it arriving just shy of 5 hours late.
Had I stayed on that 787 I can pretty much guarantee you it would have been the last UA flight I'd have taken this year. I have no future bookings and I would go out of my way to book away now, even to pay more for reliability. They just can't run a "safe, clean, reliable" operation. Safe and Clean I'll give them. Reliable, nope.