Don't know much about other Diplomacy rating methods, although I did read this, http://www.playdiplomacy.com/forum/viewtopic.php?f=565&t=34913 , the PlayDip Elo FAQ. (I haven't played there much so I have no feel for how good or bad the ELO ratings seem.)
One thing they mention that I didn't like, which is the possibility of draws lowering your rating. I think if you draw or win, you should at minimum get 0
. Although potentially losing points might force high-rated players to play for a better result, it probably also dissuades them from joining a game in the first place. It's not a perfect solution though, since the possibility of being eliminated by a group of much lower-rated players also weighs heavily if you really care about your high rating.
Not sure how it works in vDip, I should probably have a look at the code... or does anybody know the vDip rating equation?