This is a much needed counterpoint to the rabid right. Michael Moore is a frothing liberal who can muster as much spit and lather as Rush or Ann or G. Gordon or any of those other radio, TV and print hatchet artists. Like these commentators, his arguments aren't really to be debated (although he at least provides sources that actually match up to what he says in his text), but to be soaked in, so you can gather the rightous fury that you need to actually motivate you out of your lounge chair and into doing something.
You can learn things from this book. Some of them are trivial (like George W. Bush's three arrests--I think he gets to hold the record among the 43 presidents on that score); some aren't (the U.S. is number one in the number of international human rights treaties not signed).
One thing Moore does that you would never see from his counterparts on the right is that he doesn't hesitate to criticize those of the liberal persuasion, as he is as damning of Clinton's environmental and business-friendly record as he is of Bush the Lesser's. You certainly won't find strong criticism of Bush in the current political right bestseller, even though it is warranted.
This isn't a book to pass to your conservative minded friends, though, because not only are they going to dislike the message, they're going to hate the messenger and how he delivers the message. Keep this one to yourself and open it up every time you need another jolt to remind you why you need to be out there working the polls to make sure every vote is counted.