Lest anyone unfamiliar with the phenomenon assume I am overstating the fanaticism of Shamrock Shake devotees, let me direct your attention to...
...a message board for confirmed Shamrock Shake sightings around the country. Believe.
(One of the saddest recent reports from Illinois, echoing █████'s disappointment, reads: "got one with whipped cream...it was only half-full of the glorious green stuff...I was very sad.")
UPDATE:Okay, that disappointed message-board entry I just quoted? Turns out it was posted by none other than █████ herself! Small world here on the intertubes. ::g::