Salon has a piece entitled "The rise and fall of an American beer," a somewhat cursory cultural history of Anheuser-Busch. The woes for A-B are presented as thus:
Budweiser is seen as kind of like 'The Man,'" says Eichelberger, a serious student of beer semiotics. "People who want to be anti-establishment, they're more comfortable with Miller."
For the same reason, Pabst Blue Ribbon is the cheap beer of hipsters in the funky-but-not-quite-scary dive bars of our largest cities.
Chris O'Brien at Beer Activist has a more informative piece enititled "Beer and Climate Change." In it, he charts the carbon footprint of New Belgium's Fat Tire. It turns out, it's mostly "downstream" factors to blame, that is, what happens after the beer leaves the brewery. Retailer refrigeration is the main culprit, with some improvement possible through the use of closed door coolers (or, presumably, no coolers at all). Drinking at local brewpubs or (preumably) homebrewing would also help. Non reusable glass bottles are a problem, but transportation isn't much of one.