All current ebuilds for net-misc/gip list dev-cpp/gtkmm as a requirement. This is not sufficiently specific, as there are THREE available slots for gtkmm (1.2, 2.0, 2.4). gip-1.2.0.1 uses gtkmm-2.0 API, so the requirement must be: >=dev-cpp/gtkmm-2.0 <dev-cpp/gtkmm-2.4 I have seen bug 79418, where a new 1.2.1.1 version is now available, which uses gtkmm-2.4 (which is still marked testing on all platforms, although I don't know why), so when bumping this will be different.
Note, it also requires sigc++-1.2 (different slot from sigc++-2.0)
Oops, sorry - that is dev-libs/libsigc++-1.2
Re-assigning the bug, the assignee has retired.
Fixed in cvs, thanks for reporting!