WordPress.com added a feature that displays a "Like" button, at the bottom of blog posts, which, when clicked, shows a Gravatar image for all the bloggers who liked it.
"When you "like" a post two core things happen. First, author sees your "like" and can click-through to your Gravatar profile. Second, clicking "like" saves post in "Posts I Like" section of dashboard. If you're interested in keeping track of how many likes your own blog posts are receiving, there's a new "like count" column on "Posts > Edit Post" screen. This show you the total like count on each of your posts, right next to total comment count," explains Andy.
If you'd prefer not to display likes on any of your blog posts, you can turn them off under "Appearance > Extras." You can still enable or disable likes selectively on individual posts through "Show likes on this post" checkbox when editing or writing a new post.