Michael Marx loves Barq's root beer. He frequently wears a Barq's T-shirt. He brings Barq's root beer to parties. So it should come as no surprise that Mr. Marx, 34, of Gilbert, Ariz., keeps a blog dedicated to Barq's. "I've been drinking Barq's for 15 years. It's my beer," said Mr. Marx, who started his blog, thebarqsman.com, last year to collect news about Barq's, commercials he likes for the...