There was a time when Google’s service updates would regularly break their sites on Windows Phone, not to mention routinely deliver a poor level of service.
It seems those days are over, as YouTube’s latest mobile update works rather excellently on Windows Phone 8.1
The update places the emphasis on subscriptions, with a whole tab dedicated to it. The 3 tabbed interface unfortunately does not support swiping, but otherwise looks perfectly at home on Windows Phone, and the site otherwise appears fully functional, except for uploading videos, but switching to desktop mode, and with new file system access, this is very easily dealt with.
With a website working well, do we really still need an app?
See some screen shots below: