We've already discussed this.
Comments left about achievements and activities will have a "like" button, and a "flag" button, and you can do one or the other. The more people "like" something, the more that author's "karma" goes up. The more people that "flag" it, the lower that author's karma will go. If you flag something, it will disappear from your view.
Once some quantity of people "like" something, the author may get an achievement of some kind, or an extra karma boost. Or, if a quantity of people flag something enough times, the moderators will step in, permanently delete the post, which will give the author an even bigger negative karma "hit".
If your karma gets low enough, we might start restricting your actions on the site, like making you wait longer between posts, or stopping you from posting at all for a while, or issue a temporary ban, etc.