For what it's worth (apparently nothing, since YouTube/Google don't seem to care), I just wanted to add my voice to the growing crowd of dissatisfied users. I've been happily using YouTube and Gmail/Calendar/Reader with two separate accounts for as long as I can remember. My original YouTube account remained signed in all the time, but I always like to logout of my Gmail/Calendar after I've finished using it for security/privacy reasons. I come across a lot of YouTube videos when I'm going through my RSS feeds in Google Reader, and I use the 'watch later' button most of the time, and for the past however many years, I've been signed into Reader with my original Google account and when I click 'watch later' it added my videos to my YouTube account. So I think this all went wrong when my Firefox upgraded itself, but all my cookies got deleted the other day which has messed up all my YouTube/Gmail sign in stuff, and now I can't be logged into the two things simultaneously. Let me be quite clear: this is very annoying. I don't want to be persistently signed in to Google Everything with one account. I don't want all my Google searches linked to an account, and I don't want my Gmail and YouTube to be linked together either. As so many other people have already said, I tend to use my Gmail/Calendar etc. for mostly work and professional-related things, whereas YouTube is where I watch silly cat videos and things of personal/politcal interest. I do not wish these two things to be linked together in any way.
So Google/YouTube - please listen to the 100s of users who are posting on here with their complaints (and there are no doubt many more who haven't yet found this thread). You make life easier for many of us in so many ways with your various offerings, so please stop making our online lives so complicated with these silly new changes.
Any chance of an official response to this thread from a YouTube rep?