Permissions/security on pg_* tables?

Is it normal/desirable for any user to be able to select (haven't tried
insert/update) in the pg_* tables?

Is it possible to GRANT/REVOKE on the pg_* tables? It seems it is. How
can you see the permissions if \z doesn't work on the pg_* tables?

Given a multi-user environment were each user (and the sysadmin) values
security quite highly, what is the best way to secure PostgreSQL as
tightly as possible (not just looking at data in tables, but general
snooping around)?

In pg_hba.conf under "host" the second parameter is "dbname". Is it
possible to have a list of databases?

Ie:

host db1,db2,db3 10.0.0.3 255.255.255.255 crypt

Or is it limited to (all|samename|onedbname)?

Thanks for your help,
Dax Kelson
Internet Connect, Inc.