That group led me to The Great Pop vs. Soda Controversy webpage, which tracks and maps responses on whether carbonated beverages should be called pop, soda, coke or something else. Data is plotted based on respondents' hometowns.
I'm fascinated by this because back in college I noticed that Minnesotans generally said "pop" while some Wisconsinites said "soda." Since I grew up in Minnesota and my girlfriend (later wife) grew up in a soda-speaking area of Wisconsin, controversy arose every time we went to the grocery store. I felt vindicated by pointing out that the aisles were usually marked as "pop," but she found some counterexamples. We occasionally saw them described as "soda pop," which seems to bridge both camps. But I would argue that the fact that it's never called "pop soda" indicates that "pop" is the noun and that "soda" is the adjective, meaning that "pop" is the primary term.
I notice that Wikipedia is noncommittal, with the main entry being "soft drink" with a parenthetical "more commonly known as soda, pop, or soda pop." Even more fascinating is the link to the article on "soft drink naming conventions," which tracks what fizzy drinks are called around the world. In Canada, "pop" is more common than "soda." The Arab world calls them mashroob ghasi, meaning literally "gas drinks." In South Africa they're "cool drinks." In many places "lemonade" refers to clear carbonated drinks like Sprite or 7UP.
Of course, while all of this is sociologically and linguistically fascinating (at least to geeks like me), it shouldn't obscure the fact that fizzy sugar water has little nutritional value and is one of the primary culprits behind childhood obesity, diabetes, tooth decay and the like. I'm glad to see that more and more school districts are banning pop machines from their schools, or are at least having incentives for alternatives (i.e., pricing water or juice more inexpensively than pop). So whatever you call it, it's best to avoid it.
At any rate, I was glad to see that "pop" seems to have triumphed over "soda." The Pop vs. Soda site concludes that people who call it "pop" are "much, much cooler."
(Don't even get me started on the game known as "Duck Duck ______." It appears that the majority of society has uncritically accepted the conventional "Duck Duck Goose." But as we Minnesotans know, the truly orthodox and educationally superior way to play it is "Duck Duck Gray Duck." As noted on Wikipedia:
Duck Duck Gray Duck is played in the north central part of the United States, specifically Southern Minnesota/Twin Cities and surrounding areas. Two versions of the regional rules exist. In the first, the 'picker' will describe the 'ducks' as different colors or adjectives — for example, 'blue duck', 'white duck', 'lazy duck'. It's more of an educational game than an alteration of the original, in that one not only recites colors, but also tries to say 'gray duck' as casually as possible, hoping to deceive the gray duck and gain time. The second version is played exactly as the original, with the picker saying 'gray duck' instead of 'goose. The adjectives add an element of psychological warfare amongst the children, because they can insult the circle, confuse the circle with 'May Duck' or 'Gray Puck'. All of these add depth and layers among the seemingly child-like game.But to be fair, in our crosscultural Minnesotan-Wisconsinite-Illinoisan family, we play it both ways with our kids.)