vacuum questions

Currently running v7.4.8 postgres on a RHE Linux 4.0  box.  Will be
upgraded to postgres 8.2.x sometime this fall.

Several of the tables in the database that resides on this system have
lots of inserts and updates.  Very little is deleted at this time, as
the database is intended for archiving.

Currently a cron job runs a vacuum analyze  3 times a day.  Is there any
need to run a vacuum full every so often?
If so, how often should a vacuum full be done?  And do all other
processes that "hit" the database need to shut off when a vacuum full is
done?

Also another office that has a similar setup has switched to running
pg_autovacuum instead of the vacuum analyze 3 times/day, are there any
advantages and/or disadvantages to this approach?

Thanks in advance for any information and guidance you can give,
Julie