Funny...several years ago I switched from UA to US. UA lost my luggage. It was never found. Then they told me that I must have a receipt for every item lost in my luggage (this was back in 97). They never gave me a penny or even an apology. Not even we are sorry.
I got tired of their crappy customer service. That is why I switched to US.
I also got tired of the rude employees at IAD and ORD.