So, you’ve read that Mountain Lion now has Twitter deep integration much like iOS, but how do you actually set it up?
Start off in System Settings, then into Mail, Contact & Calendars.
Here, along with the usual email offerings, you will find a new option for Twitter. Select it and then you can simply enter your Twitter username and password.
Once you’re done you will find that Twitter start to pop up in sharing options, like the sharing icon in Safari (pictured).