libwmf-0.2.7 changes the name of a library (namely, libwmf-0.2.so.6 becomes libwmf-0.2.so.7) which causes ImageMagick to break. Other programs that use libwmf might also, but I haven't seen any other breakage yet. It might be good to symlink libwmf-0.2.so.6 to libwmf-0.2.so.7 in the ebuild. Recompiling ImageMagick against libwmf-0.2.7 fixes this.
this is due to libwmf using the libtool flag "-release". this flag binds anything compiled against libwmf-0.2.6 to version 0.2.6. i've written the libwmf maintainer to see why -release is used. as best i can tell it should not be. i'll update this when i hear from him.
putting this on hold. portage should soon be able to address this type of problem.