Same here. I'd like to see real data. Personally if you are spamming me and I want to unsubscribe, having the word "quit" will likely hasten my decision in much the same way I'd like to hit something and smash it if I am frustrated.
Exactly the same for me. When I have already reached the decision to stop receiving emails those words would be an even stronger indicator that "quitting" is exactly what I want!
I'd be interested to see some stats from some a/b testing on this.