I just emerged media-fonts/libertine-ttf on PowerPC (Apple PowerMac G4 MDD, Motorola 7455 Dual 1 GHz --> PPC 32-bit) with ACCEPT_KEYWORDS="*", because of the missing "ppc" KEYWORD in the ebuild. Other than that the font works fine on a newly installed Gentoo 2007.0 on this architecture. REQUEST KEYWORD "ppc" added to media-fonts/libertine-ttf-2.7.9.ebuild.
jakub, i'm not sure how you interpreted this as a stabilization request...
~ppc'd. Thanks for testing :)