For awhile, you had the option to display only your username on Youtube. Now it seems that your real name, as set on your Google+ account, will be visible to other Youtube users. The option to use your username has disappeared.
http://i.imgur.com/90DUvFD.png
Also, it appears that your real name is fixed as "public" on Google+ and cannot be set to "circles only".
http://i.imgur.com/90DUvFD.png
Also, it appears that your real name is fixed as "public" on Google+ and cannot be set to "circles only".