I submitted a multiplayer yahtzee like a year ago, it worked perfectly for the 20 concurrent users my version of smartfoxserver supported. It eventually got flagged, I think because I used the standard interface for the chat, but of course the game was programmed by me.
From what I could tell from the reviews, the people that got a chanse to play it, liked it very much. But until I can afford a full version of smartfox that supports unlimited users, and a good server to run it on, I wount be submitting any more multiplayer games.
You can try the multiplayer yahtzee here. Have fun, and bring a friend if there's no one playing! =)