It's significant in terms of sheer numbers of people -- at $15 a ticket, we're talking a potential audience of 4.3 million people and counting. No US documentary has ever pulled in these sorts of numbers before. Again, my hat goes off to Michael Moore.
It's true that Leftists often forget that Hollywood is a small (and often surprisingly progressive) piece of a very complicated and very multinational media landscape. The real money is in advertising -- last year, the US ad market was $120 billion, I think, or 1.1% of US GDP. (Half of that was in print advertising, incidentally, proving that the death of the text is highly exaggerated). That's more than ten times larger than total US box office revenues in 2003, which were about $10 billion.
-- DRR