Cool indeed. However, it would be abused and go down hill REALLY fast. One of those things that is only good on paper.
In lieu of such I choose to respond with the CORRECT info and usually a quick retort.
I could see it being abused yeah. This feature is actually added on yahoo answers. You have some trolls on there that just boo the person even if the info is correct. Plus if you don't like the answer the best thing to do obviously is not kudos the post.