Interesting and good to know. I grew up in Boston where "you guys" was common, and I believe it still is, though possibly that's been changing over the last five years (during which I've lived outside the US). I only ever lived in Massachusetts/Rhode Island, and I've heard that "you guys" isn't as popular in other U.S. regions. In the U.S. South, for example, they've used "you all" or "y'all" as the plural for a long time.