Installed are the dead symlinks /usr/lib/graphviz/python23/_gv.so /usr/lib/graphviz/python24/_gv.so /usr/lib/graphviz/python25/_gv.so from which only the 2.4 one should exist - as I have only Python 2.4 installed - and point to /usr/lib/python2.4/site-packages/libgv_python.so
Fixed in media-gfx/graphviz-2.16.1-r4. Thanks for the report.