Apple’s new OS for Macs integrates deeply with Twitter, which makes it seamless to send tweets and check updates that mention you from your followers. OS X Mountain Lion will also update your contacts with their Twitter account info.
You first need to add your Twitter account (you can set more than one), in the Mail, Contacts & Calendars panel in System Preferences.
If you want to update your Contacts to include their Twitter names, choose your Twitter account from Mail, Contacts & Preferences and click Update Contacts. Where Contacts can find someone’s Twitter name, it will be listed in a separate category.
This fall, Facebook integration comes to Mountain Lion, to coincide with the expected release of iOS 6.