My first and only op-up was on MSP-PDX in 2005. I was on my way to interview the next day, and my connecting flight had come in late, I ran to the gate, as the gate agent closed the doors. The gate agent automatically re-booked me on the next flight.

I had no status, I did not ask for anything (I was a kettle, I wouldn't have known better)

When she handed me the boarding pass it still didn't dawn on me until I actually got to my seat in 2B, on either an MD-88/MD-90.

That was GREAT... I made myself useful by ordering a Gin & Tonic for a PDB :-)