When vaccuum full should be performed with postgresql-8.1 and autovaccuum?

[Arnau <arnaulist@xxxxxxxxxxxxxxxxxx>]

Hi all,

  I'm migrating our DDBB from postgresql 7.4 to postgresql 8.1. In 
postgreql 7.4 we don't have autovaccum running. So, every night before 
doing the daily backup we do a "vaccuumdb -f -z" for each DB. My doubt 
is, the autovaccuum  with the version 8.1 is started by default and I 
don't know how often I should perform the "vaccuumdb -f -z" or now it's 
not necessary to do it at all.

Thank you very much
--
Arnau