I don't find the word to be an unusual one at all among educated people. It is ever-so-slightly affected in that it separates the more educated from the less. I would never expect to hear a stereotypical beer-swilling, stockcar race affectionado, wife-beating, trailer-park inhabitant to use 'beyond my ken'--educated exceptions to the stereotype aside, all three of them.

Now I wonder: Why would the more educated use 'beyond my ken' in conversation instead of 'beyond my knowledge' if not to separate themselves from the masses and to declare (by implication) "Hear! Hear! [by my implication] I am educated because I am not using the word 'knowledge,' but the word 'ken' instead. Aren't I a very clever fellow?"

As Consuelo once pointed out to me, there are ways of knowing someone is a 'smarty butt.'