ProjectViewer's "archive project" action only supports compressing projects into a jar file, including options to add a manifest and ignore .java files. This is very java-centric and not terribly useful.
I think PV should scrap the name "archive project" and provide several different methods to "export" a project, possibly as a service provider for other plugins, but not necessarily. A standard "compress to zip" option would be more universal than archiving as a jar, and then two jar options could be supported: a standard one, and an executable one.
As one possible scenario, PV could come with just a "compress to zip" export option and provide exporting as a service. Then a number of different java-specific export options could be defined by JavaSideKick or a new plugin (e.g. JavaProject), such as jar, executable jar, javadoc, etc.
As a counterpart to exporting, being able to import an archived project would also be handy. As an example, right-clicking on a group would provide an "import project here" action that would prompt for the archived project and a target directory. PV would then unzip the project to that location and import all the files into a new project.