Easter Eggs in quizzes

I sometime use Easter eggs in my quizzes. How often do you use?

I usually use on famous people. For instance, if this person is well-known by certain nickname, fave hobby, a place he's associated with.

I've never used sequential unlocks but I'm keen to use it in future. E.g. In a history quiz, correctly identifying the year of the October Revolution or writing "Bolshevik" could unlock all of bolsheviks in that particular quiz.