PostgreSQL 8.3 - issues with autovacuum
I can't find any evidence that 8.3 autovacuum is buggy. Autovacuum has been improved in 8.4 with free space maps which obsoletes some parameters which:


  (when set incorrectly) could make vacuum less effective


so with 8.3 it is important to set them correctly.
The postgres wiki says (and I'm inclined to agree):


  As of 8.3, autovacuum is turned on by default, and you should keep it that way. 


and:


  The answer to almost all vacuuming problems is to vacuum more often,
  not less, so that each individual vacuum operation has less to clean up.

As you say, "adding entries to pg_autovacuum does the trick" when autovacuum needs to be tweaked - but just be aware that "pg_autovacuum [is] not saved in database dumps"