RDEPEND=">=x11-libs/gtk+-2.0 >=dev-libs/glib-2.0" gtk+:2 glib:2 for future gtk+-3 migration.
Are you sure this won't build with gtk+-3? (if I don't misremember, gtk3 shouldn't break as much as qt3 -> qt4 migration, and it's more like a gtk+-2.22+cleanups, but maybe I am wrong)
If gtk+ 3.0 will be API compatible with gtk+-2.0, then it will go to SLOT="2" like current one, unless someone does something stupid.
Umm, ok, it's more future proof
+ 27 Mar 2010; Pacho Ramos <pacho@gentoo.org> + -files/gtk+extra-2.1.1-fix-row-deletion-segfault.patch, + -files/gtk+extra-2.1.1-glib2.10-full-fix.patch, + -files/gtk+extra-2.1.1-glib2.10.patch, gtk+extra-2.1.2.ebuild: + Install documentation in proper place (bug 311599), don't install useless + INSTALL file (bug 311601), drop no longer used patches (bug 311605), use + SLOT deps for gtk+ and glib (bug 311607), stop inheritting no longer used + eutils.eclass (bug 311609), switch license from GPL-2 to LGPL-2. Thanks a + lot to Samuli Suominen for noticing all the problems.