This plugin has been brought up to date with the Solr/Lucene 3.6 release. I've also updated the README.txt and removed the incubation disclaimer.
You can download the artifacts from http://people.apache.org/~kwright/apache-manifoldcf-solr-3.x-plugin-0.2, or find a tag in SVN at https://svn.apache.org/repos/asf/manifoldcf/integration/solr-3.x/tags/release-0.2-RC0. Vote +1 if you think this is ready for release. Karl