Hey.
One issue that my group faces when we play Ars is preserving the Medieval Paradigm, and I'd like to know how other groups deal with it. The fundamental problem is that taking a society and throwing in a major, chaotic aspect and expecting it to stay the same just doesn't work. If you have a game world that is exactly like real Europe in 1200, except there's a band of people in it with awesome magical powers, Europe in 1250 is not going to be exactly the same -- even if the PC's keep only to the strictest rules about not interfering with mortals. Things that just weren't possible with Medieval technology because possible with magic, and they are things any reasonable person would invariably want to pursue.
For example -- in one game, we had a very small covenant. Just the Magi and a half-dozen grogs, all of whom were essentially lab assistants (or librarians, or bookbinders, etc). As a result of the small size of the covenant, everyone in it could read -- something the Magi took advantage of for the sake of convenience. When new grogs arrived one or two at a time and the covenant grew, it rapidly became irritating to not be able to leave these new people chalk notes or written directions, so the Magi required all new arrivals to learn how to read. As the covenant's library grew to include several books on useful trade skills, it was proposed that we should allow all our covenfolk free access too these trade books. After all -- the more skills they know, the more valuable they are as laborers...
Oops, we just invented the public library and universal literacy a few hundred years early. @#$#!
Things like this, accidental or otherwise, can seriously move the feel of the game away from medieval paradigm. On the other hand, preventing this from occurring at all would be unrealistic and makes the game feel artificially constrained. How do your groups deal with this?