Here's a quick code snippet on how to backup files and restore them from the shell.

To back them up, run the following code:

$ tar -zcvf filename.tar.gz folder/

$ tar -zcvf filename.tar.gz .

$ tar -zxvf filename.tar.gz

Upgrading from Joomla 1.5RC4 to Stable (Production) was a breeze. There was no need to make changes to database structure or anything. Simply download the full stable release, upload to my server, and overwrite the files. Here's how I did it from the shell.

Navigate to the proper directory:
$ cd /mysite/

Download (wget) the new compressed file:
$ wget http://joomlacode.org/gf/download/frsrelease/5078/21064/Joomla-1.5.0.tar.gz

Uncompress over old files:
$ tar -zxvf Joomla-1.5.0.tar.gz

Remove the installation directory:
$ rm -fR installation

I then visited the site to check to make sure everything was working. Sure enough, it all worked great! I would highly recommed creating a backup of your site files and database. Here are some links from my site on how to do this from the shell:

Create a MySQL Backup from Shell
Create file/website backup from Shell

The following is a short code snippet on how to view which MySQL databases are available for a user, then a command to back them up. This should work on Unix and Linux variants.

To view what databases are available to be backed up, run the following command:
$ mysql -u root -h localhost -p -Bse 'show databases'

To backup each database, run the following command:
$ mysqldump -u root -h localhost -pmypassword databasename | gzip -9 > faqs-db.sql.gz

There was a very small issue with the DS-Syndicate module that broke the W3C Validation compliance. The img tag did not end with a forward slash. To fix this, simply open /modules/mod_ds-syndicate.php and on line 51, column 64 add a / to the end of the <img> tag so the line looks like:

$mod_content .= "<img src="/" . $feed_img . "" alt="feed image"/></a>";