After playing with gentoo-osx I came across
this usefull link
which explains how to properly manage the usage of masked packages. Aparently
if you create /etc/portage and in there create a package.keywords file.
The entries go .
This is quire usefull, and should be used instead of ACCEPT_KEYWORDS.
It will allow you to properly maintain a system as stable using
a limited number of unstable packages.