playBunny: 6 moves/day would be totally unworkable, because you do not know when your opponent will move. Imagine a player from Europe (say Germany or France) vs someone from California. Say both players are both online from 9 AM till 9 PM, their local time. Player in Europe moves first, at 9 AM his time. Californian player moves as soon as he logs on. Now the European player plays his second move. But it's already 6 PM *his* time - three hours to go and five moves to play. If the Californian player plays at a rate of 1 move an hour, the European play will time out.

With players scattered around the globe, it hard to make fair time controls. And time controls that gives less than 24 hours/move will be unfair to one of the players.