let's kill off /etc/make.profile: it's inconsistent with the rest of portage's configuration and easily forgotten. As profiles are in the tree and make.profile can only be pointed at real files and not e.g. ${PORTDIR}/profiles/default-linux/amd64/2006.1 it just gets worse. Having a PORTAGE_PROFILE var in make.conf would be so much nicer... It makes switching PORTDIR far less of a pain.
While I like the idea this is -dev material (affects much more than just portage).