1) for blogs/discussions/comments
2) for members
3) used in the leaderboard app for rating members (I have found that the current leaderboard system is no longer available except to those who already had it before it was dropped, therefore it may not be upgradeable. There was discussion though of a replacement app in the future)
This could be either a like/dislike or rating system. I personally like the wikis that provide a 5-star rating system ... just click on one of the stars to rate.