Hm, it's hard to say. A lot of people said he kind of strategically edited his documentaries. But, even if he did, it definatly makes a lasting impression. Personally, I have both his books, and have seen/own all his documentaries. (Had to download bowling for columbine) I really enjoyed all of them. I think he's really opened a lot of people's eyes to a lot of things.
There is this kid in my English class who HATED activists. But, our teacher showed us some of Michael Moore's documentaries (The Big one, and Bowling for Columbine) and he kind of got a big kick in the head of "hey, maybe everybody isn't a dumb airheaded jock that lives on easy street, and never has to work for anything." He was a lot more bareable after that. =x