I came across this issue while inspecting the USE flags that my 
Playstation3 uses. And I couldn't disable some of those (cups, ipv6 and 
some others) so I looked at why they were forced upon me. Turns out the 
top-level make.defaults for ppc, x86 and amd64 (and maybe other 
architectures as well) add cups to the USE flags. I would understand if 
cups was added somewhere under the desktop/ profiles, but force it upon 
all users? Similraly, 'ipv6' is added in the 64bit-userland ppc profile, 
which means forcing it on for everyone who is running 64bit userland on 
ppc. I at least have no interest or need having ipv6 support and again, 
I would understand if ipv6 was only added in one of server/ profiles or 
some place further down the tree.

(I brought this issue first to #gentoo-powerpc and I was told I should 
bring it up in releng. Since I can't talk in the IRC channel, I'm 
sending the mail here.)

thanks
tom