The way I see it, DV appears "cold." It was used to enhance the feelings of despair and isolation the characters felt. The bleakness.

The last five minutes are shot on 35mm film. Film appears "warm." Not to give away the ending or anything, but with the infected dying out, there was hope for the survivors. The use of films reflects this.

That's my viewpoint. I doubt it was anything to do with being "hip," but it's speed and ease of use was a definite contributer. Just listen to the commentary on the DVD and see how much was shot in Danny Boyle's back garden.