I really want to get my hands on Day Z. In fact I was [this] close to buy the Arma II pack when I read there will be a standalone version of the game soon(?).
I hear people complain about asshole bandit players though and I understand that. First thing that pops in my mind, without even having played Day Z, is that there should be some cons for being a bandit.
For example: People who witness a "murder" (ie from a distance) get the ability to warn other people about the bandit through warnings on billboards and [fill in clever idea here]. This adds a new level of excitement for the murderers but also for decreases the amount of bandits because you don't want to become hunted. How will the game recognize you didn't witness a murder but someone protecting himself from the murderer? Now that's a clever question.