YouTube now tests the header that's already displayed in Google Search, Gmail, Google Docs and many other Google services. The header shows your Google+ notifications, a box that lets you share videos with other Google+ users and links related to your Google profile.
Right now, the Google+ header is only displayed if you haven't created a YouTube account and you log in using your Google account (so you don't have a YouTube username and channel). Obviously, you need to join Google+ to see the new features.
{ Thanks, Michael. }