All non-passive YouTube users (ie: anyone who wants to leave or reply to comments on videos) must now create a Google+ identity and link it to their YouTube channel.
Cynics (such as myself) are seeing this as a nasty piece of *evil* blackmail on the part of Google as it attempts to boost the numbers of G+ users and the levels of activity within the G+ community.
Unfortunately, in doing this, Google seems to have completely forgotten the KISS strategy that made their search engine so distinctive and a darling of Net users everywhere. The YouTube comments system was also very simple, very clean and surprisingly effective.
Now however, users must fight their way through the acres of dross that are associated with a Google+ account and although the new system offers a few extra features, much of the essential core functionality of the previous YouTube comments system has been destroyed.
There are presently several online petitions demanding that Google reinstate the old comments system and numerous "rant videos" from upset YouTube users but perhaps the best demonstration of how poorly this forced change has gone down is the like/dislike ratio and the nature of the comments on Google's own YouTube promotional video for these changes.