He hacked it up a little, but dude used my post on his poll results section:http://espn.go.com/blog/afcnorth/post/_/id/27764/flash-points-franchise-turning-events
It was funny actually - Immaculate reception was leading as defining moment, but nobody was posting comments in favor of it. Which probably means most of voters were non-Steeler fans, and that was the one thing they knew about. But I put one out there and actually felt it was true. Prior to that play, Steelers had been to exactly two playoff games in their entire history with zero victories.
Other contenders were hiring Noll, and 1974 draft (don't remember fourth option, but got little support). Which were important events without question, but not "defining" in my book.