I answered 8, but only 5 of what I thought of were in the 8 provided as the answer, so the real number is at least 11 and it was pure luck that the number I reached was the "correct" one chosen by this QotD's author. Hugo pointed out some more and 2 of his were not in my 8, so that means the answer is at least 13 - or at least 12 if UPDATE is excluded.
It's an amusing question, but I don't know what the answer is in reality. Fun answering it and reading the discussion, but not really a learning experience.
I agree with Hugo's comment that this sort of thing doesn'r really work for QotD, because whatever number anyone comes up with we can't be sure that it covers all possibilities.