After Google demanded Microsoft to take down their YouTube app due to the lack of ads, YouTube has finally returned to the Windows Phone platform—with ads included.
The updated version, which had Microsoft and Google working together, now also features video upload support, the ability to stream live video channels, voice search and activation, as well as access to playlists, uploads, video lists, and the ability to manage a YouTube account’s profile page. Windows Phone users will be able to pin Live Tiles of videos, channels, playlists, and search queries on the Start screen, too.
Source: The Verge
UPDATE (as of August 15, 2013):
Google seems to have disabled the YouTube app for Windows Phone yet again, citing that it still violates their Terms of Service.