I flew American on a trip to New York about 2 months ago and after the plane has been airborne for about 30 minutes already, an announcement was made over the loud speaker that the plane had to turn around from where we came, because there's something wrong with several of the systems. No need to panic, we were in no danger, but we're turning around.
I knew things weren't that bad since we were not told to assume the crash position.
After a 3 hour delay to get a replacement plane in the middle of the night, we were off again. No meal comp, no meal at the plane, just ""Shut up and enjoy what I give you!"" was American's attitude
Cons: assume the crash position.