All I can say is ha ha ha ha ha ha ha, but sometimes you get and sometimes you don't. Remember, the game first rolls for drop or no drop, then magic, then rare, then set, then unique (I left out normal stuff huh). How much magic find you does matter. When I do MF runs I always find stuff. However, sometimes the "boss" drops diddly squat.
Try it yourself. Give something (a run) 20 tries and see what happens. But write down what you get so you can evluate. I found Arreats Face from a minor boss in the Cold Plains and then went to go kill Andy, (in hell) but she didn't drop anything. Oh well.
The drops from Mephisto and other bosses are affected by mf. I think the reason those five people told you "mf doesn't matter" was because Blizzard's statement before 1.10 was released, which said that mf will from now on not work on bosses. This is incorrect. I've heard this from reliable sources (people who have read the game code).