DOTA 2 actually has a system where you are only able to "report" 3 players a week (maybe a day, can't remember exactly), or "commend" 6 players a week, so it adds more value to each. You can "report" a player for negative communication, intentional feeding (basically repeated dying on purpose), and one other thing that I can't remember...or you can "commend" them for being either friendly, forgiving, teaching, or showing leadership.
I've only played about 90 DOTA 2 games with other human players and I have about 20 positive feedbacks. I think limiting the number will make everybody feel each time they report or commend somebody carries more weight. Obviously, they'll need to include more than 3 negative and 6 positive...DOTA 2 games can easily go over an hour, and I may only play 6-7 in a week, but you can play 20 games of Halo without even thinking about it. Also, if I report somebody and action is taken against them, when I log back in to the game, it actually TELLS ME THAT! You get a message pop-up saying "thank you for your feedback" and telling you they have recently taken action against somebody partially based on your reporting them. Also, they don't ban people from the game for these reports, they just give them various levels of communication bans which eventually subside...and in a game based on teamwork, a communication ban is pretty bad to anybody who actually cares about winning.