There's another forum I go to that uses a similiar system and we haven't had any problems.
Although I do like how they've laid it out a bit better.
When you click to applaud or boo the post, another screen comes up asking you to explain why in a quick sentence or so.
You can also click on your profile and have the options of seeing Who changed your karma and who's karma you've changed, which shows every single posts that's been ranked as well as why it was ranked that way.