I think that there should be an option to display the title of the site along with the thumbnail. The URL usually has no significant relevance to a site that I would be looking for. For example, an article on zen may be hidden away at someonesname.blogger.com and the article would look like any other page with a lot of words on it. However, the title might include zen in the name, and thus would be easier to find if one were able to see the title of the site along with the thumbnail.