Searching only for the latest manifestation of the pumpkin spice phenomena, we collected all geotagged tweets in the continental United States for September and October 2014 with references to either "pumpkin spice" or "#psl", yielding a total of 19,537 tweets. But rather than simply mapping the basic distribution of these tweets, we've instead normalized this data by tweets referencing "coffee" during the same period. Using a 25% sample of all of these coffee-related tweets -- totaling 42,696 tweets -- aggregated to hexagonal cells, we calculated the odds ratio at the lower bound of the 95% confidence interval in order to provide a bit more context and account for any number of biases within the data. Using this measure, we've identified those places with greater-than-usual numbers of pumpkin spice latte tweets relative to those tweets referencing coffee (orange), and vice versa (purple), as seen in the map below.
References to Pumpkin Spice Lattes relative to References to Coffee 
 Well, actually, Renee Kaufmann had this hunch. All credit for the idea behind this post goes to her.
 Sorry about the Web Mercator projection, y'all.
 Can one still wear a belt with yoga pants?