Our United flight connecting us between Newark and St. Louis was cancelled after we had checked our bags. According to United, the flight was cancelled due to "flight conditions" which is normally translated to mean "weather." After learning of the cancellation, we quickly booked a SW flight for the same route at roughly the same time. That flight left a few minutes late, but got us to our destination on the same day.
This was not our first United cancellation for dubious reasons. Although I must admit, our bags arrived on time on the first available United flight the next day.