There are a buttons at the bottom of each hub. But, out of those 9 you can share a hub at more than 9 places. The link button, you can write a snippet and place link on blog, website, or hub. Then there is the blog this button where you can also add the link which is built in the title of more than one of your blogs, but you do need to write a snippet iin blog, otherwise a blue colored title is all that shows. Then at the top, Google Plus button if you click on it, and are member of google plus, you can send a hub to the public, to those in your circle. Also, at the bottom of each hub is a share this with followers, which reaches multiple people.
Digg brings zero traffic to me. Reddit is worthless too. I am seeing an increase through Stumbleupon and using the Google plus button.