Ok, I don't use Facebook either, but I do use youtube. I don't have my real name associated with my account, and I only watch, not produce videos, so nobody would see my face. I uploaded a hand drawn face as my avatar.
I do have a real gmail account that I use for official business, but I never log into it with firefox. I keep an instance of chrome for all my real-world/real-name transactions that I don't use for anything else.
But I finally gave in and let google have my real phone number for password verification, both my real name and my pseudonym are now tied together by at least that. ( they probably had me pegged before that dispite polipo etc, but now they do for sure. )
Now youtube keeps asking me if I want to appear as blank picture ( MyUserName ) or my avatar picture ( MyUserName@gmail.com ). Though I would like to appear as my avatar picture ( MyUserName ). That's not a choice. So I choose a blank avatar. It was a cute hand drawn avatar that now nobody will see.. .
I think the thing to worry about is if you've already given your info and your identity is outed by some site you've signed into. If they know your real name, they can out you some day, so don't do anything interesting on their site.