app-office/calligra[postgres] blocks the removal of dev-libs/libpqxx-3.1 which in turn blocks GCC 4.7.
I haven't found anything in the Calligra documentation that states a particular version for libpqxx.
Please review Calligra for the possibility to move to the recent dev-libs/libpqxx-4.0.
+ 02 May 2012; Andreas K. Huettel <email@example.com>
+ calligra-2.4.0-r1.ebuild, calligra-2.4.1.ebuild, calligra-2.4.9999.ebuild,
+ Relax libpqxx version dependency since it seems to work fine with 4.0, bug
Nuff said. :)