I had an issue with the current ebuild for 0.3.0.018 in that the compile for cel-ps (ebuild file cel-ps-1.1-r2592.ebuild) would go smoothly and then the install would fail during the execution of the command "jam install" citing access violations (I am guessing it didn't deal well with being in a sandbox since this same command worked when done independently of Portage as the root user, but this is where I don't fully understand how emerge works). The "install" command was receiving permissions errors related to creating directories and files in /opt/planeshift/cel and no amount of adjusting the permissions of anything under /opt would remedy this problem.
Because the cel ebuild from your ebuilds for 0.3.0.017 (ebuild file cel-1.1-r2592.ebuild) didn't give me this problem, I modified the cel-ps-1.1-r2592.ebuild file to resemble the installation method used there, then rebuilt the "Manifest" file and again ran "emerge planeshift". Once I did this, cel-ps built and installed without a hitch on my system.
http://causality.ifastnet.com/psbuild/cel-ps-1.1-r2592.ebuild is my modified /usr/local/portage/dev-games/cel-ps/cel-ps-1.1-r2592.ebuild file.
If you replace/modify this file, then be sure to run this (as root) so that emerge won't fail due to mismatched checksums:
ebuild /usr/local/portage/dev-games/cel-ps/cel-ps-1.1-r2592.ebuild manifest
Also, once all dependencies were successfully built, the building of Planeshift itself failed because its Manifest (file /usr/local/portage/games-rpg/planeshift/Manifest) indicated an incorrect filesize for
http://loux.thefuture.free.fr/distfiles/planeshift-0.3.018.tar.bz2. To fix that, I edited the Manifest file and corrected the expected filesize. My modified file can be downloaded at
http://causality.ifastnet.com/psbuild/Manifest.
Once this was done, everything built with no problems and installed smoothly. The only possible "gotcha" was that after all the installation was done, the subsequent "etc-update" wanted to modify "/etc/cel/vfs.cfg" by adding two obviously incorrect entries that contained the /var/tmp/portage temporary working directory from the ebuild. I am not sure what caused this one, but it was easy to catch and the etc-update option of "2) Delete update, keeping original as is" took care of this.
For convenience, I also made a tarball of my /usr/local/portage overlay, which is loux's original work (from
http://loux.thefuture.free.fr/portage.tar.bz2) plus my modifications mentioned above. It's available at
http://causality.ifastnet.com/psbuild/my_overlay.tar.bz2.
I am definitely no expert in Portage, so let me know if any of the above looks like a bad idea

but the above changes made this work out for me.