I think there are a lot of (older) projects which started with the native Hibernate API and native XML mappings.Now, it's the question of how to migrate to JPA 2.1 without pain.

What would be really useful is a Hibernate to JPA 2 migration guide both at the API, query and mapping level.
Does the book provide guidance for such a migration path?

For example, is it possible to use the native/proprietary Hibernate XML Mapping files with JPA 2 at the API level assuming Hibernate as persistence provider?

Will the book outline features of Hibernate that are not yet available in JPA? (custom collection types come to my mind)