Ogion - you only carry a grudge from game to game if you are so immature that you carry a grudge from game to game...
On the contrary, I may make the argument that being stabbed by a fellow player will make me jut as likely to ally with him the next time in hopes he uses his same stabbing skills on someone else to further our alliance.
But more to the point, being stabbed by someone - regardless of who it is - is a lesson that I should always be on guard for a stab. Therefore, instead of holding a grudge, I thank the player for teaching me a lesson, and hopefully I become a better player moving forward.
Being the consummate asshole that I am in the forums, if I feared metagaming I would play no games, for the majority here probably have "cause" to take vengeance on me.
But, this is a fantastic community, and most of those I have played with take their gaming seriously, and take each game uniquely.
Get a few games under your belt before you cast aspersions on this awesome, high-caliber gaming community, my friend.