I too am looking foward to MP games. Can you imagine how much fun it will be to marry off your children to each other. I can see all the conversations players will have with one another negotiating a marriage. I doubt this will be in the game, but what if we could exchange items like gold, troops, or even entire counties to one another. "I'll agree to a marriage between my son and your handsome, hefty daughter in exchange for 200 gold pieces (by the way, does anyone know if the currency issue was resolved?) and a little province called Roma!!" This kind of negotiation would be very interesting and could add the element of manipulation and deceit. As a vassal to another MP player you could promise your support in the coming war, but you've been speaking secretly with a neighboring duke who will gladly recieve you in to his Duchy. Then you switch sides. Great stuff.
One question. Will the purchase of relics be an event in the game, and if so will this add piety to your realm. I'm guessing a relic like the bones of some great saint will cost quite a bit though. This would also increase pilgrimages to your churches, which would hopefully create extra revenue.
Have we ever gotten a official announcement on the number of provinces in CK, I'm very curious.