I have a customer that is about to undertake a migration of an Oracle 11g database to PostgreSQL 9.x (exact version to be determined). I am talking not only of the migration of schemas and data, but also of a substantial codebase of Pl/SQL stored procedures, as well as many triggers.
I don't think they know yet what they are up against. Everything I have read is that this is a very substantial effort. At this stage, they would be particularly interested in realistic and practical information on how to estimate the effort required as well as any best-practices or guidance on transition strategies.
I have found official documentation on the PostgreSQL site for porting Pl/SQL to PL/pgSQL. This is excellent technical documentation. However, there success will require that they are well prepared realistically understanding the scope of the effor they are asbout to undertake.