Good question! Before submitting to blogs, users are required to filter the list by genre. They can then sort by the # of fans that outlet has, or -- even more handy -- there's a notes column in the far right that gives some vital statistics. You can see it here: http://i.imgur.com/pqMky6h.png
If you visit the "directory of blogs" page, you'll see a full selection of the filters: http://www.submithub.com/blogs