High Availability PostgreSQL HOWTO article

Has anyone implemented the HA solution linked
<http://www.taygeta.com/ha-postgresql.html ) linked> on the PostgreSQL
Technical Documentation Web site?

http://www.taygeta.com/ha-postgresql.html
<http://www.taygeta.com/ha-postgresql.html>

I have read through the article, but one concern I have is that I don't
see how this is any different than performing a "File system level
backup".

In the PostgreSQL 7.2 Administrator's Guide, under the Backup and
Restore Chapter (9) - they mention the restriction that the database
"must" be shut down in order to get a usable backup.

How is taking Rsync copies ever 5 or 10 minutes any different than
taking a file system backup without shutting the database down?

Eric Comeau