Here are Digg’s official descriptions of these two new key features:

Notifications: No matter where you are on the web, you can discover popular Digg stories and stay up to date on what your friends are Digging, submitting and commenting. These notifications are fully customizable. Within your preferences you can track different categories and media types, and turn notifications on or off.

Digg Toolbar: Displays Digg counts & comments as you browse around the web. You can also Digg and submit stories directly from the toolbar, which is collapsible to save space. Note that the toolbar respects user privacy by passing only hashed URLs to Digg to check if they’ve already been submitted.

Overall I’d say it was a lot more unique than I was expecting, so if you spend a lot of your day going back and forth on Digg, this toolbar is for you.  You can download the new add-on on Digg.com.