This happened to me a couple of weeks ago.
I had a C+ aisle seat on my flight home, but had to do a last minute change to another flight (work related, not DL's fault). I ended up with a middle seat, because it was the only choice to get home that evening.
When I got to my row, there was someone else in my seat. The guy immediately said his wife was on the window, would I mind seating on the aisle? I took it.
But it seems that to a couple of FT'ers, that was a grave transgression as he was sitting in "my" seat.
To those couple of folks: would you have really booted the guy "on principle"?
Anyway. Enjoy the rest of the thread, I'm out.