This plugin allows you to change the Author slug, without having to actually enter the database. Assuming you are an admin or a user with the "edit_users" capability, you will see an extra field on your user edit/profile edit page. This allows for greater security, as your user name isn't revealed through your URL structure. It also allows you to make your URLs look a bit cleaner. (i.e. - http://example.com/author/username/ could become http://example.com/author/user-name/)
Plugin Home:
http://wordpress.org/extend/plugins/edit-author-slug/