upgrade requires dump/restore?

While reading FAQ at
http://www.ca.postgresql.org/docs/faq-english.html#3.10, the following
advice is given:

"The PostgreSQL team makes only small changes between minor releases,
so upgrading from 7.2 to 7.2.1 does not require a dump and restore.
However, major releases (e.g. from 7.2 to 7.3) often change the
internal format of system tables and data files."

Our question is, how do we determine if we need a dump/restore or not?
 We have several hundred boxes that are currently running 7.2, and
we're in the process of putting together a new software update that
will (among other things) upgrade the database to 7.2.3.

Is a dump/restore required from 7.2 to 7.2.3?  What if we were to go
from 7.2 to 7.2.4, or even from 7.2 to the latest, 7.3.2?  How can we
tell when a dump/restore is required?

Thanks,

Stephane Charette
stephanecharette <nospam> at telus <nospam> dot net