I had some disappointments on my first class trip back from Vegas (first world problems, I know) but I had paid for a first class seat and the seat didn't recline, there was no meal for me (they were short a meal and I was the last one asked) and my bags came out at the end of the delivery -- so, three things that are supposed to distinguish first class.

I emailed and expressed my disappointment in a pretty courteous way.

And they sent me a $100 travel certificate!

So win-win -- I'm satisfied and I get to use it on another United flight