Performance differences using varchar, char and text - Mailing list pgsql-general

In the Postgres 7.3.3. User Guide section 5.3, it says that there's no performance difference between the three type.
  But in 'PostgreSQL Database Performance Tuning' by Jean-Paul ARGUDO (section 5: use correct datatype), it says there
is a performance difference because of you might need more I/O to read the data (which makes sense).

So, is there a performance difference?