Magento Upgrade Process

The Magento upgrade process should include clearing out the files in the $MAGENTO_ROOT/var/cache/ and $MAGENTO_ROOT/var/session/ directories, or else some really odd errors show up, including this:

Fatal error: Call to a member function getBackend() on a non-object in /home/$USER/public_html/app/code/core/Mage/Eav/Model/Entity/Collection/Abstract.php on line 379

http://www.magentocommerce.com/boards/viewthread/27119/

In the Upgrading Magento wiki entry, it does mention that:

"Delete var/cache and var/session directories"
http://www.magentocommerce.com/wiki/upgrading_magento