Apparently, the ebuild wants linux headers which are less than 2.6.16 (or so), which aren't in the tree any more, so portage pulls in 2.4 headers. This causes various block conflicts. The problem in the appears to be a workaround for bug 148438, which works around the xfs headers redefining some primitives. This no longer appears to be the case, and using kernel headers 2.6.30 or greater (didn't check 2.6.27) allows netatalk to compile.
punted http://sources.gentoo.org/net-fs/netatalk/netatalk-2.0.5-r1.ebuild?r1=1.8&r2=1.9 http://sources.gentoo.org/net-fs/netatalk/netatalk-2.1.ebuild?r1=1.2&r2=1.3 http://sources.gentoo.org/net-fs/netatalk/netatalk-2.1.3.ebuild?r1=1.1&r2=1.2