The title of Morgan Spurlock's new documentary asks a pretty good question: Where in the World Is Osama bin Laden? Spurlock says he didn't necessarily expect to get an answer, only to use the question as a means of opening a larger conversation. Even so, it elicited a range of responses from the people he spoke to in various suburbs and villages across North Africa, the Middle East and the Asian subcontinent.

Some of those interviewed in the film just laugh. Others take the enquiry at face value. "Ask his family," advises one shopper in a Saudi supermarket. "Bin Laden is not here," says a woman in Pakistan, "but his influence is here." "F*** him," spits an old man in the Afghan mountains. "And f*** America." The insult is directed more at US policy than at Spurlock personally. Almost every civilian he meets, and several of the zealots and combatants, appear to get along fine with the film-maker himself.

"When you travel overseas, you become the face of your country," says Spurlock. "I was conscious of making that a friendly face, especially when I was the first American that a lot of these people had ever met. I finally took my mother's advice, and just listened to what others had to say."

Spurlock's critics tend to like him, too. Even those who argued that he was stating the obvious with his first film, Super Size Me, in 2004 - which recorded the gruesome but unsurprising effects on his health of eating nothing but McDonald's for a month - did not dispute that he came across as a good guy. They said the same about his television series 30 Days and are now saying it about Where in the World Is Osama bin Laden?

"A film like this gets attacked for everything it isn't, rather than what it is," says Spurlock. "I'm trying to make films that transcend the typical documentary audience. I wanted to take the viewer on a vicarious trip, where you learn things as I learn things. That doesn't go down well with people who don't think they've got anything to learn."

To put this another way, Spurlock does not make documentaries for critics, academics or New York intellectuals. He lives in Brooklyn but still considers himself a country boy from West Virginia. "I come from a really small town, the most normal, most American environment you could imagine," he says. "I used to go hunting in the woods with my grandfather. The people I make films for are the kind of people I grew up with."

This is why he provides historical and geopolitical context by means of silly cartoons and musical montages in the new film, at one point staging a video-game fight between himself and bin Laden. "It's a way of dealing with a serious issue in a funny way," he says, "and maybe engaging the average viewer in a way that TV news is failing to do."

Spurlock appears to measure his own success in these terms, maintaining that the greatest end result of Super Size Me was not the fact it became one of the most profitable documentaries ever, nor even that it appeared to effect actual change in the fast-food industry (McDonald's phased out its supersize menu just as the film was gaining publicity, although the company says this was a coincidence, and has condemned the film as a distortion of its policy). No, he says, the most important thing was how it impacted on regular people - and not just Americans.

He tells me about a man who approached him recently on the London underground, showed him an old photo from his wallet and said: "That was me six stone ago." Here Spurlock puts on a woeful English accent, presumably for the sake of verisimilitude. "Because of the film," he says, "this guy had looked at how he was living and eating and changed it. To me, that shows the value of documentaries. They can empower people."

He has similar stories to tell about Where in the World: the young man who was inspired to apply for his first passport after seeing the film; the mother who had her first "political conversation" with her teenage son after they watched it together. There is no way to verify these anecdotes, but Spurlock gives you no particular reason to doubt them. Like the even wealthier documentarian Michael Moore, he is sometimes accused of being disingenuous in speaking to and for the general public, but in person and on screen he more often seems earnest to a fault. His wife, Alex Jamieson, became pregnant while he was planning this project, and her due date is used as a narrative device in the film, as he promises to return from his travels before the baby is born.

To Spurlock, this is not mawkish or manipulative but honest. "When we found out Alex was expecting, that's when this film was born for me. No pun intended. It obviously made me ask what kind of world we were bringing a child into, and it made me want to go and meet other guys like me, who are about to have a kid or are trying to raise young families in places where life is a lot more dangerous."

In this respect he finds what he is looking for, and the resulting domestic scenes are what give his documentary a thesis. As Spurlock goes to dinner in a working-class Moroccan household on the same street where a group of local teenagers recently became suicide bombers, or sits around a camp with Afghan villagers and their children, their conversations become genuine cultural exchanges, suggesting "regular people" may speak a common language the world over.

"Oh, completely," he says. "The heart of it is, the majority of the planet is made up of reasonable people who just want to get on with their lives. All it takes to screw that up is one crazy person to walk into Tel Aviv and blow themselves up, or one settler to fire into the West Bank."

If this sounds simplistic, Spurlock seems to think that's no bad thing. "Sometimes we need to be reminded of the simple seeds from which complex ideas grow."

As for finding bin Laden, the closer Spurlock and his crew came to the tribal regions around Peshawar, the more people seemed to know where he might actually be, and the less they seemed to care. "There were plenty of people pointing us toward Waziristan," he says, "although nobody gave us an actual address, like 13 Cherry Street. In places like that, you get the feeling of how important bin Laden is, but also how unimportant he is. In the end, he's just one man."