Last year when singer/songwriter Dave Carrol was traveling to Nebraska for a one week tour his flight with United had a layover in Chicago where Dave and his band Sons of Maxwell, and several other passengers witnessed baggage handlers on the ground throwing guitars. Dave's $3500 710 Taylor Guitar was badly damaged as a result.
Efforts to have United Airlines take care of the damages resulted in 9 months of wasted time with United Airlines stalling at every turn. You can read Dave's version of the story here.
As for me. I don't fly all that much, but you can be sure that I probably won't choose United.