4 is in the works, but probably isnt enterprise ready quite yet. If you have a short time to market, I would say use 3.2x
Thanks a lot Bradsdavis, But what about the version 4 features? It seems that version 4 supports command-based services, database partitioning per process language, and specially full embeddability.
Incase someone comes accross this, the features for jBPM 4 will be rolled into jBPM 5 based on user feedback. jBPM 3.2.x is the supported JBoss branch.