I have been reading and thinking a lot about advancement in Role-playing. It is one of the most common reward systems that is put into a RPG (others being things like fate points or whatever you call them), and as such I think it should be considered what you are rewarding.
Kill monsters/gets XPs is a fine reward if what you are aiming for is a game of monster slaying. What I am thinking though is that rewards should be given for “bringing the cool”. The game most responsible for this line of thought is The Shadows of Yesterday with its system of KEY events and player KEYS used to generate the experience.
If a player does something cool in keeping with their character concept they get X advancement points, if another player does something cool in the same scene that is character appropriate AND plays off the first players cool then BOTH characters get X times 2 experience. If a third gets in on this and fulfills the criteria then all three get X times 3 experience and so on.
This of course raises the question of “how do you determine what is cool for the character?” I think this would be answered by using a system similar to the KEY system in TSoY.
Anyway, this is just some pondering..