@Chrispminis: The grey check mark takes a measure of control away from the player. The game is about politicking, and otherwise making others believe that you are their friends. If they know, with 100% certainty, that you're entering moves at the same time as their enemies, they will inevitably be suspicious. The time at which you enter your moves should not have any bearing on the game as long as you are entering them!
@idealist: I don't really care about Facebook changes. I was not one of the people who hated the "new" Facebook, and there have been several. Instead, I complain when it needs to be done. Geofram has made his point clearly, consistently, cogently, and I can't believe that I'm agreeing so much with somebody from the Internet. Further, the grey check mark brings with it all the baggage that finalising early does, so if you're worried about wasting your supports, you can ask your ally to finalise.
Nobody can deny that it alters the dynamic of the game. Like them or dislike them, the rules of Diplomacy generally stay the same. This design change alters a fundamental mechanic of gameplay. The simplest question is "Did Kestas intend to alter the mechanics of Diplomacy?"
If that answer is no, this feature should be removed, or modified so that only the owner can see his own grey check marks.