The Seam reference doc, Chapter 3.4 "Seam managed transactions" shows how to set up a Seam managed EntityManager, which is injected to Seam components via the @In annotation.
However, most sample code I've seen use the @PersistenceContext annotation. Any difference? Could I use the @PersistenceContext annotation outside of an EJB3 container?
@PersistenceContext is used to inject a transaction-scope or stateful-bean-scope persistence context, according to the EJB3 spec. This will work with Embeddable EJB3.
Seam managed PCs are used when you want a conversation-scope entity manager or Hibernate session.