I daresay most airlines have their up and down days. I've had good experiences with AmericaWest for instance, and most lately it's my impression that Alaska Airlines has steeply deteriorated in service, reliability and friendliness. But MOST recently I booked a flight with Northwest, a non-fancy but reliable and friendly enough airline. Weather was due to come into Boston about two hours AFTER the plane was due to land. So Northwest cancelled my flight due to weather, stranding me for 24 hours in Minneapolis at my own expense. Don't know whether I'm going to write a letter or not, cause after all I made it to Boston alive and that's something.
I don't hold a brief against United. The one airline I really hated was Pan Am, and TWA went bad just before it went broke. When the money runs low it's hard to keep up appearances.