gnumeric depends on =gnome-extra/libgsf-1.10* which causes libgsf to up- and downgrade on every emerge -uD world. This shouldn't happen, either gnumeric needs to be fixed to work with current libgsf, libgsf should be slottet (if possible) or libgsf >=1.10.* should be masked.
The fix for updated libgsf is here: http://bugs.gnome.org/show_bug.cgi?id=308047
Don't use stupid --deep, this is a perfectly valid dep & this can't be slotted. Actually the buglink indicates that all current apps that dep on libgsf may be problematic and should be fixed, it may just not be discovered yet. *** This bug has been marked as a duplicate of 96179 ***