Once. In 2008. From NW. GA at DTW skipped over me for an upgrade because I was not at gate when she cleared them. It was my first complaint email ever. Perhaps that what merited the call.

I will say that DL does the whole email CS thing way better than AA. Sent in three emails to AA in the last two months. Two praises, one complaint, asked for responses on all. Only response was an obviously computer-generated one to the complaint, about 3 weeks after I sent it.