This year we came up with a point system to limit the amount of time the kids played games on the computer and get them to do more educational things. I've written up the details in an article called A Point System for Earning Computer Time.
Overall, it's worked very well. I would encourage parents to come up with their own system so that kids earn the privilege of playing on the computer rather than give them unfettered access. I'm not against playing games on the computer but rather believe kids should indulge in a wide variety of play with a strong preference for the real world.
This point system doesn't have to be just for computer time. I think of it as an alternative currency and you can invent other things they can spend the points on. My golden rule is that there is no exchange rate between points and real money. I also never deduct points as punishment as that would destroy trust in the system.