This is a follow-up to my last post on integrating Drush with my Drupal Scripts Library.
I have just added the script drupalManageDrush.sh which will install the Drush library in a subdirectory of the directory in which the Drupal Scripts Library is installed. It will also set up the environment and provide a shortcut command ('ddrush') in the bashrc_drupal.sh file (which is meant to be called from your .bashrc file).
Once this is in place, you should be able to run Drush commands against your sites with the command:
$ ddrush <sitename> <drush commands and parameters>
Now, you should be able to reliably use the Drush command set (like update!) w/ your Drupal installs.