I just got back from watching the film and thought I'd add my thoughts.
Whilst there is evidence that Moore is spinning facts, I'm not in the least bothered by it. I've read his first major book and began reading the second, when I realised I didn't want to because it was the same thing again. The film is in the same vein and I knew a lot of the early facts based on the books. However I still enjoyed the film. I think Moore's use of music is fantastic and the selection of material is powerful. Whilst you have to take things with a grain of salt, it's still very informative.
I think films like his are needed because they offer perspective. Whilst Moore may be guilty of spinning the facts, so is everyone else. It's propaganda, but it offers a different side to what we are normally fed. It's like the angel-devil scenario. If you have one of them on your shoulder all the time, telling you what's what you're going to get a one sided look of things. To put some propaganda from one side into perspective, you need to get some from the other.
I think the message of the film is that troops are dying for something which isn't worth fighting for. I think the bit towards the end with the mother at the White House where she confronts the other woman is extremely powerful and reflects his point perfectly.