I'd never really heard that phrase until recently, and it put me in the mind of the phrase Living Constitution, and what with emanations of any pneumbra being part of the Living Constitution, the phrase Living Magisterium seemed a little too close.
Only referred to in that way by Catholic liberals on Freepnet as far as I can tell.
Catholics where I live don't even know the word "Magesterium", the vast majority of whom voted for John Kerry and support same sex marriage. But this is just in my neck of the woods (Mass.)