I wore shorts and flip flops with a t-shirt back in August while on vacation with my wife and daughter (she's under 2). Flights were wide open. An rj flight canceled. My flight ended up having one seat. I was in shorts and a t-shirt so we did not get on. Got on the next one. I then missed three flights in a row from ATL to home. I was called up to all of them to tell me there was one open seat (none of the non-revs ahead of me wanted to split up). We ended up getting on the last flight of the night. Had I been dressed in business casual, we would have been on every flight we tried (me in jumpseat with wife and kid in last seat). My days of traveling out of business casual are over. I'll commute to work in jeans and a collared shirt sometimes with pants on top of my suitcase on standby just in case, but that's my only exception.

At NWA, you had to be in business casual to be in first class, but it was not free. It seems like NWA had more first class seats available though. At Delta, I have seen 70 paying passengers on the upgrade list for 0 seats. What good is free first class if Delta just gives the seats away to paying passengers anyway? It's really frustrating on oversold international flights. Delta does upgrade passengers internationally when it runs out of coach seats. I have seen this first hand.