'so' as a sentence opener began in Silicon Valley. Michael Lewis in his book The New New Thing, published in 1999, noted that 'When a computer programmer answers a question, he often begins with the word so.' Microsoft employees have long argued that the 'so' boom began with them..." In any event, whoever's responsible for this annoying affectation probably shouldn't be bragging about it, There are times, though, when "So" sounds exactly right. The first known use of so as a sentence opener is from Chaucer's Troilus and Criseyde: "So graunte hem sone out of this world to pace." (So grant him soon out of this world to pass.) Some might wish the same for the overuse of so these days, but it's most likely here to stay. So. Back to the matter at hand. You know the drill. There were 16 cases of Interupt* (for interrupt*) in OhioLINK today, and 372 in WorldCat.
(Geoffrey Chaucer reading his poems to the court of Richard II, frontispiece to Troilus & Criseyde, c. 1400, Corpus Christi College, Cambridge, from Wikimedia Commons.)