With blogs implementing the idea that the web can become a conversation, the concept of providing personalized badges that let you express your character are having visible viral effects. Well known examples include Flickr Zeigeist, Feedster top 500 and Bloglines shared subscriptions.
One such site I recently found is the Cyborg Name Generator. You choose your name and your graphic and it gives you the HTML code to insert into your blog. According to the creator Lore Sjöberg the details matter as he describes on his blog he made one small change and it really took off especially among live journal users.