I find that when someone is losing, the tendency is to take turns at the last minute. Conversely, players want to take turns more quickly on games they are winning. A small bonus is points should be given if players take their turns in less time (within10 hours for example). This in turn will have people visiting the site more frequently and players will be more motivated to finish their turns earlier in hopes of gaining this small bonus. This im sure will result in less missed turns and more participation on the system overall.
Elias