We already highlighted 10 secret features of OS X Mountain Lion, but another hidden standout is the ability to link Twitter handles to all your contacts with a single click.
Before Mountain Lion, you had to enter in Twitter handles for each contact one-by-one, but this new method involves a simple click in your system settings. Here's how:
Open up System Preferences.
Click on Mail, Contacts & Calendars.
Choose Twitter and sign in using your Twitter credentials.
Click "Update Contacts..." and Mountain Lion will begin updating your contacts to include their Twitter handle if they have one.
Now you'll be able to right click on a friend's name in Contacts or Mail and select their Twitter username to send them a direct message or view their tweets.
Deep Inside Mountain Lion: 15 Hidden Features in Apple's New OS | Wired