Moving to steadily towards a Hibernate Search 4 we just released Hibernate Search 4.0.0.CR2. In total we managedto address 32 issues. If you are interested in the details have a look at the Jira release notes.
On top of internal API polishing and the obligatory bug fixes we focused on bringing the documentation up to date. Have a look at the latest version. In particular we tried to highlight the role of the new IndexManager interface. Each Lucene index is now managed by an IndexManager instance and, except of the use cases of index sharding or sharing, there is a one to one relation between an indexed entity and an index manager. Luckily these architectural changes have no effect the basic configuration and use of Hibernate Search :-)
Make sure to also read the Hibernate Search Migration Guide when trying to upgrade to Hibernate Search 4.