well for me the borat movie is something like a field experiment. petzold's comment at the top of his post is relatively valid, i'd say though: those people appearing in the movie were caught by suprise and were completely unsuspicious at first. that in itself creates an imbalance. but i say this is exactly the method of borat's experiment.
cohen once (i think it was on late night with conan o' brien) said that the only way to a) get together with the people he wanted to meet for his borat "series" / movie  and b) to have them lower their defences is to create selfconciousness and unsuspiciousness (??) so his interviewees wouldn't act but rather say whay they actually think.
that said, personally i don't think that we shouldn't elevate borat's work near the realms of science. i think he just tries to expose some of the traits of a few individuals (i don't mean this in a pegiorative way) living in certain parts of the country which might be fun to watch for people in other parts of the country with different backgrounds and, of course, especially non-US viewers.
for me it's basically like with political caricatures in newspapers. they hurt and even offend some people (see recent incident with the mohammed caricatures), they make others laugh a bit but if you distill their content down to the one or two essential things you might gain some insight - let it even be biased insight - into an area you might not have see that way before. the key to understanding the movie and not being offended by it even if you are a US citizen is to realize that borat doesn't offend the nation. a movie by a comedian is too insignificant for that. he merely takes a look at various individuals who sometimes do exhibit a strange attitude, sometimes don't.