On the USE variable howto there is a link to a page listing up-to-date USE variables available, pointing here: "http://www.gentoo.org/doc/use.html", but the page is not available and I can't seem to find it. (There is no use.html in http://www.gentoo.org/doc/en or http://www.gentoo.org/doc either.
I learned from another/similar bug that I submitted that this and the other bug were both submitted while in the middle of the site being updated. Fixed now, I've seen.