Most (all?) of the ebuild I have through g-cpan depend on dev-perl/module-build which is no longer in portage.
Bug 97639 is when it got added.
Steps to Reproduce:
Can you please elaborate? Which version of perl, which packages?
I just tested with perl 5.10.1-r11, your version of g-cpan and the CPAN package Geo-Coder-Yahoo, no dev-perl/module-build anywhere in the ebuild...
Cannot reproduce w/ g-cpan 0.16.0. Please provide more information about your system and a reproducible testcase.
As far as I can tell it works for me too now.