It looks like media-libs/gstreamer-0.8.x (as well as all the 0.8.x gst-plugins) has recently been switched to hard masked in gentoo's portage. media-libs/gstreamer 0.10.x and associated plugins are still OK.
I couldn't find any info when I searched gentoo's forums, but this often happens prior to removal from the portage tree.
Does anybody know if that is what is happening with these packages?
Sabayon has a package (media-plugins/libvisual-plugins-0.4.0-r2) that has a specific dependency on the 0.8.* version. Amarok has a dependency on libvisual-plugins. This package (libvisual-plugins) seems to be the only package that still has a dependency on the 0.8.* version. Everything else uses the 0.10.* version or above. Oddly, the version of libvisual-plugins in gentoo's portage tree does not have a depency on gstreamer at all.
As an experiment, I unmerged all the 0.8.* gstreamer and gst-plugin packages (leaving the 0.10.* packages alone), then edited the ebuild for Sabayon's libvisual-plugins, and modified the gstreamer dependency to accept any version of gstreamer. It re-built OK, and Amarok still seems to work fine.

