Ah, oh wow. They're pushing heavy. Google+ isn't all that great to be honest, you're not missing out on much. But I'd be annoyed to no end about those notices.
I've got two active Google accounts. In FireFox I am logged into one, which includes Google+ and in Chrome, logged into a different one that I mainly use for YouTube and gmail. I never get the notice on my alternate one, but looking into it, I've already got a G+ account for that too. I don't recall setting one up, but I must have.
Wish there were more Google alternatives. Vimeo, DailyMotion and LiveLeak are all great and all... but still very small content as compared to YouTube.