More than once is all I'll admit to. Its easy to do, especially when you're in a rush.
Once at the track and pressed for time, I capped the race "in line". When I got to the window I used the wrong number and didn't notice till I got back to my seat. I immediately ran back to make amends but the race went off.....My "wrong" pick WON and paid over $400. That's the only time I ever made out on an error.