I came across an interesting article on Yahoo! that discussed documentary film maker Michael Moore's movie making practices, with criticisms and his responses.
I watched a film about Moore about a year ago, and I cannot remember the title of it, but I do recall that it did show some highly questionable tactics in Moore's editing. Also, if you read the linked article, you'll see that Moore claimed that Cubans have a higher life expectancy than Americans-- Which is true, but it is only a difference of one tenth of a year. So Moore did engage in sensationalism there. My advice is: Never trust a movie. Always find the original peer reviewed articles and read them yourself.