I saw this was discussed some in the ELO thread. There is a huge difference to the gameplay depending on if the ranking system gives you a rank based on where you finish or if it gives you a rank based on win/loss.

The current way you have an incentive to try to come in 5th rather than 6th, for example, so you end up ignoring the big guys once they've gotten a lead and wage your own private war against other smaller players. This is kind of interesting, but very often it becomes clear who is ahead and very little will change it. Also, the difference between 5th and 6th is often determined arbitrarily by whoever is ahead or bad starting position.

Conversely, if it were an all or nothing sytem there would be much more diplomacy because everyone would have to constantly attack whoever is ahead. Also, any alliance that gets formed will have to eventually be broken, so there is always the question of when the backstab will come. If every player is vying for 1st or nothing, then there is a self-regulating aspect to the game. Also bad starting positions will be somewhat negated because there is much less incentive to pick on the little guys, since bringing down the big guy becomes priority #1.

Each method has it's advantages, but I think an all or nothing/win-loss ranking system would make the gameplay much more interesting.