I just read Paladin's interesting article on the XP system in Dragons at Dawn. According to the article, Dave Arneson did not award any experience points for killing monsters or taking their treasure. Instead they were awarded for roleplaying only.
In my opinion XPs are a useful tool in encouraging the players to behave in certain ways. I can think of few players who really need encouraging to go out and kill things and take their stuff. Arneson found a way around that. Worth thinking about for any campaign.