The Mail, Calendar & Contacts preference is the place to set up all of your e-mail and Calendar accounts, it now also has the added Social Media accounts such as Twitter, Facebook, Flickr & Vimeo.
Adding these accounts makes it a lot simpler to upload or share stuff through these sites, system wide.
A brand new System Preference for 10.8 is the Notifications Preference.
This is essentially just the same as the one on iOS, and gives you options over what type of alerts you receive from all of the various applications on your Mac
Usually the default options for each app are fine, the one thing I would recommend doing however is re-arranging the list so that the apps important to you are at the top of the Notification Center
If you haven’t discovered the Notification Center yet, its accessed by clicking on the notification icon in the menu bar, the 3 dots and 3 lines in the very top right hand corner.
If you have set up your Facebook account, then you will also have a box at the top of this to post instantly to Facebook.