John81's post in How Does The "like" System Work? was marked as the answer
I think everyone has something like 20 or so "likes" they can give out per day. Whenever someone clicks "like" on a post they like that adds to the count which at set points changes the tag from neutral to the next tag and so on.
It was mostly put forth so people could express their like of a posting without having to make a post saying nothing more than that when they didn't have anything else to add.