With the new YouTube interface, some of the screens/options have changed.
This page shows you where to change the services you share videos, favorites, likes, comments, etc.
First, log in to your YouTube account and then go to
http://www.youtube.com/account_sharing
or click on the Settings under your account menu (top right). Then click on Sharing on the left menu. This should be the Sharing and Connected Accounts page.
Click on “Connect” next to the the accounts you want to connect such as Facebook, Twitter, orkut, or MySpace. Ofcourse connecting accounts requires you to have, and log in to, the accounts.
Click the checkboxes next to items you want to share like Comment on a video.
Click Save Changes.
That’s it.