I have blackdown-jdk-1.3.1-r1.ebuild installed and while the USER path is correctly set
to have access to /opt/blackdown-jdk-1.3.1/bin, the ROOT path is not set for this and
some java ebuilds (jndi-1.2.1-r2.ebuild is the one I ran accross) use the 'jar' command
without setting the PATH.
Contact me if that didnt make any sense (it has been known to happen).