Manning has a nice early release of “Solr 4 In Action” online. Technically it’s just “Solr in Action”, but since it talks about SolrCloud, ZooKeeper, etc, it really is about Solr 4.
One of the things I like are the diagrams. The authors took their time with these, including callouts.
Chapter 8 talks about Facets and Data Analysis, and follows some of the themes author Trey Grainger also covered in his Lucene Revolution talk. The book also follows the more modern convention of communicating with Solr via JSON instead of XML, which will appeal to Ajax/HTML5 developers.
Be advised, this is a preview release, so not all the chapters are available yet. This is Manning’s “MEAP” program.