We are getting closer and closer to the final release of Apache Lucene and Solr 4.0 as a few minutes ago 4.0 beta of Apache Lucene library and Solr search servers were released.
Full list of changes in Apache Lucene 4.0 beta, compared to 4.0 alpha version, can be found at the following address: http://wiki.apache.org/lucene-java/ReleaseNote40beta. The full list of changes in Apache Solr 4.0 can be found at the Solr wiki as well: http://wiki.apache.org/solr/ReleaseNote40beta.
In order to download Apache Lucene 4.0 beta library please go to: http://www.apache.org/dyn/closer.cgi/lucene/java/. Apache Solr 4.0 beta can be downloaded at the following address: http://www.apache.org/dyn/closer.cgi/lucene/solr/.
Please note that not all mirrors have to be updated yet.