Clever ad, yes.
1) now, rather than just throwing away the annoying flyer, it looks like you've got to scrape some goo off your door, too.
Maybe the pizza grease eases the removal.
2) it really only works if you're home when they stick it on. (Though I'd probably still check it out from the inside after noticing it from the outside.)
3) how much are they paying the leafletters extra to connive their way into a building and then spend the time sticking these things on?
4) Ads like this tend to backfire, I think. Sure, I'd see it and think to myself, "Yes, I'd like some pizza delivered now." But would I call Papa John's?