I have long been bothered by the expression “unbeknownst to . . .” I even see it in up-to-the-minute blogs and hear it on newscasts. I have always thought this word to be hopelessly archaic and wonder whether any of you readers share my peeve. I guess the source of my annoyance is personal–it simply grates on my ear. And by the way, “amongst” is a close second.
My advice to writers is to absolutely avoid expressions that were probably old when Shakespeare scorned to use them. The exception would be when you are writing in an archaic manner about very old times populated by very stilted people.