@AnalogyAddict I hear a lot of people talking about undeletes, but have yet to see any hard proof of it happening.
Mostly the only things I have seen are either (a) private subs came back and posts with them. Folks thought they deleted everything with a tool not knowing that you cannot edit/delete stuff on private subs, so when the sub unprivated they thought that was deleted content restored or (b) the awful Reddit cacheing, which limits how many comments are displayed on your username page (and thus puts a hard limit on how many of your comments you can reasonably find and delete).