An article in the Press of Atlantic City (NJ) does a better job of covering the surge in firearms purchases than anything I've seen in a national (or local Virginia) media outlet. The reporter, Daniel Walsh, doesn't descend to the level of depicting gun buyers as fevered paranoiacs, like so many other press accounts I've read in the last few months. An example:

Across the nation, sales of guns and ammunition have skyrocketed since November, while their availability has sharply decreased. The sales spike has been focused largely on assault rifles, handguns, shotguns and other weapons used for personal defense. Many attribute it to fears that President Barack Obama's administration could ban some semiautomatic weapons. Some also attribute the tanking economy and corresponding fears of increased crime that could accompany the newfound poverty some may experience.

That's the reason in a nutshell, and not overstated as fear of post-apocalyptic social disintegration.

[Guns in short supply as sales shoot higher - Press of Atlantic City]