Scott Mitchell writes about a neat feature he created for .TEXT in this article and this follow up article. Basically, it adds a "Rate This Content" control to each blog entry much like MSDN has for each of its articles. This allows you to let the author know just how much you love or hate the article, and hopefully provides some constructive (or if not constructive, at least humorous) criticism.
I'd love to take this one step further. Currently, when a blog supports one the CommentAPI, RSS Bandit allows you to comment on a post via a "Post Reply" context menu item. It'd be neat to create a "Rate This Item" API so that aggregators can allow users to rate a blog entry if the blog supports a ratings system. What do you think?