I've said this before, and I think this bears repeating. Nothing is going to be loved by 100% of the population. Say you have 300 people on a 747. Some might find the service on that flight very good, others awful, some may board being stressed out and nothing will please them, others may be in a partying mood and aren't too concerned about the food or the movie.
In short, different people are going to react differently. I know enough airline employees to know nobody sets out to provide bad service. I think the vast majority of people who work for airlines and are in contact with the customers genuinely want to provide good service, and I think how we the passenger approach and deal with them has a significant bearing on how we are treated. Something as simple as saying "please" and "thank you" goes a long way in the air (and as someone recently suggested turning to the F/A at the back of the plane to say "thank you" at the end of a flight is something that makes their day! I tried this last summer and I wish I had a camera to show you the surprise on their faces).
I know DL has been trying hard in recent years to mend fences after the Ron Allen debacle, and everything I have heard is they are making progress. I do admit though I haven't flown them of late but would not hesitiate if they offered the lowest fare to wherever it is I may be going.
The customer isn't a moron, she is your wife -David Ogilvy