Drush is of course the best way to manage your site, and here at Babson College we are utilizing multi-sites on the Acquia Cloud. These commands greatly simplify our account management across these many sites:
To run a drush command on all of your sites in a multisite
go to your drupal root directory ie: /var/www/html/babsondev/docroot
and then run
drush @sites user-create testuser drush @sites user-password someuser --password="gr3@tP@$s"
this will create a user on all of your sites. To get a site list you can do
drush sa | grep -v @