Director's quote

"Things have been vibrating in the air and we have tried to catch them and reproduce them," Thomas Vinterberg says. "It's hard to put into words and I can't explain why the Ugandans in the film are weightless or why it is snowing in summer in New York. It is our report on the world, our picture of the way the disasters of the world seem more and more absurd. I hope it will evoke a response in other people, and on some points reality has already overtaken the film. We suddenly hear of hail falling in the Sahara ...".
---Danish Film Institute website
http://www.dfi.dk/tidsskriftetfilm/22/itsallabout.htm

So in one sense, any symbolic analysis is just self-indulgent intellectual wankery. On the other hand, what the audience takes away from a film/book/painting has at least some validity even if it doesn't entirely jibe with the author's intent.

Plus, you know, it's kinda fun.