gnome-panel 2.8.2 wont build with evolution-data-server 1.2.x, it requires 1.0.x. But the ebuild states >=0.97.0 ... should be =1.0* ... The pkgconfig file was renamed from libecal-1.0.pc to libecal-1.2.pc.
It was correct, it's just lack in portage functionality that causes this.
Fixed in CVS. It looks like eds would actually be relatively easy to SLOT, but I can't think of a good reason to do that.