I tried to install dev-perl/RRD-Simple and it died not finding RRDs.pm. I found that it was supposed to be installed in net-analyzer/rrdtool, and apparently it won't unless it was built with USE=perl So, easy fix for RRD-Simple, need RDEPEND on net-analyzer/rrdtool[perl] ?
Whoops, clarification. The emerge/build worked fine, it's a runtime issue. When trying to use RRD::Simple in a perl script, this will fail with not being able to find RRDs.pm.
+ 27 Nov 2013; Tony Vroon <chainsaw@gentoo.org> RRD-Simple-1.440.0.ebuild: + Be stricter about our rrdtool run-time dependency; as pointed out by Ben in + bug #489196 we cannot cope with RRDs.pm being absent. That means building + rrdtool with USE="perl". My apologies for the delay here; your fix is obviously correct (which is the best kind of correct) and now in place.