Running PostgreSQL 9.0.1, with streaming replication keeping one read-only mirror instance up to date. Auto-vaccuum is on on the primary, except for a few tables which are not vacuumed by the auto-vacuum daemon, in an effort to reduce business-hour IO. These tables are "materialised views".
Each night at midnight, we run a vacuum across the database in order to clean up those tables that are excluded from the auto-vacuum. I'm wondering if that process replicates across to the mirror, or if I need to set up vacuum on the mirror as well?
Vacuum and autovacuum replicate like any other write operation. (Well, they are obviously somewhat special internally, but as far as your question is concerned, they are normal write operations.) Running vacuum or autovacuum on the slave doesn't do anything and is not necessary.