I've heard many criticisms of Fahrenheit 9/11 based on supposed factual errors. Some of those criticisms have some weight; many don't.
This article repeats a line about the Moore movie that simply isn't true:
"Central to Mr. Moore's indictment of the current President Bush is his charge that the U.S. government secretly assisted the evacuation of bin Laden family members from the U.S. in the hours following the Sept. 11 attacks, when all other flights nationwide were grounded. He supports this with grainy images of indecipherable documents."
In the movie, Moore makes very clear that the bin Ladens were helped out of the country "after September 13th," not "in the hours following" the attacks. I don't know why people keep accusing him of distorting the truth on this matter, when it's one of the less controversial claims in the film.