Auto vacuum documentation

Where is the definitive source for all things autovacuuming?  I have
seen http://www.postgresql.org/docs/8.1/static/maintenance.html#AUTOVACUUM.

Ultimately the issue I am having is that the postgresql logs show each
of the databases being 'autovacuumed' (actually quite often), but when
I click around in pgAdmin it still prompts me to vacuum for many of
the tables.  I am wondering if there are any sites that tell me the
ins-n-outs of autovacuuming.

Regards,
Collin