wp-reactions is a plugin that allows blog authors to gather a reader's gut reaction after reading a post.
At it's core, wp-reactions is designed to encourage readers to leave some sort of feedback after reading a post on your blog. Instead/as well as leaving a comment, Reactions gives readers the option of providing their 'gut reaction' to a post by providing a form consisting of a list of author-specified terms that the user can choose from.
The list of terms that a user can choose from to describe their reaction can be modified by the author to fit the needs of the blog. As a specific example, the author of a link-blog may choose to get feedback on whether readers have already seen the content elsewhere. This information could then be used to determine 'freshness' of the links.