I complained about an inconsiderate FA who didn't serve drinks to F and talked to the guy in 1B the entire flight. I wasn't expecting any compensation, just wanted to vent (it was my first ever upgrade). They comped me 5000 miles.

2 weeks later I again complained because of delayed golf clubs (2 days, had to rent clubs for the tournament i was participating in). I received no reply and no compensation. I'm ok with not receiving compensation as I'd received it 2 weeks earlier when not expecting it... but the complete lack of response bothered me. There may be a limit to how many times you can complain and be compensated in a certain time frame.

All of this was done with the "Contact Us" email form on the DL website.