14 DAY TRIAL // Google has been working towards a unified design and this applies to more than just the look and feel, it wants features to be available across services. The main example of this is the new unified header that is used in most Google products.
So far, though, YouTube has been kept separate, as it has been since Google bought the site. The video site has always had its own identity.
Even as a new design was introduced late last year, unique to YouTube, it didn't borrow much from Google's new design, that's now used by many other Google sites.
Still, not even YouTube is completely independent, it seems that the site is testing a version of the unified header seen on many other Google sites.
The header is displayed for users that don't have a YouTube account, just a regular Google account they're logged in to.
Users need to have a Google+ profile though for the new features to work; however, they can't have a YouTube account, with a personal channel, associated with their Google one.
Users seeing the new header get the regular notifications box, the ability to share something to the Google+ as well as links related to their Google+ profile, just like they get on other Google sites, including the homepage.
Those that already have a YouTube account and profile see a different version of the header, the regular version, with the searchbox, links to browser or upload videos as well as a button for their YouTube profiles.
It's unclear whether Google will proceed and introduce the unified header for all YouTube accounts. If it decides to do that, it will have to do some work to the YouTube profiles, perhaps better integrating them with Google+.
