marking as enhancement, sorry for the spam
This project has been split up. Maven now depends on plexus-utils(source available :-) )
I'm pretty sure this package is needed, and isn't provided by maven. It's listed under the project.xml, and gets downloaded during the build process. I checked the downloaded jar, and it provides the org.apache.plexus package... but I haven't been able to find anywhere to download plexus.
I managed to find plexus's subversion after some digging: http://svn.plexus.codehaus.org/ I've added a package to the experimental for plexus-utils.