Whoops, the title got truncated. I meant to say that Hibernate is reportedly "agressively closing" the JDBC connection.
According to http://jira.jboss.com/jira/browse/HIBERNATE-32, "For an application server JTA datasource, always after_statement is used to aggressively release connections after every JDBC call".
This seems to have the side-effect that for a stateless session bean, the rule is, one trip to the database per method invocation. Yikes. For real?
Better to take this to the hibernate forums for now.