7 uses of MAINTENANCE_MODE in Drupal 6

drupal_flush_all_caches in includes/common.inc

Flush all cached data on the site.

drupal_get_css in includes/common.inc

Returns a themed representation of all stylesheets that should be attached to the page.

drupal_get_js in includes/common.inc

Returns a themed presentation of all JavaScript code for the current page.

drupal_goto in includes/common.inc

Send the user to a different Drupal page.

update_flush_caches in modules/update/update.module

Implementation of hook_flush_caches().

_drupal_bootstrap_full in includes/common.inc

_drupal_maintenance_theme in includes/theme.maintenance.inc

Sets up the theming system for site installs, updates and when the site is in off-line mode. It also applies when the database is unavailable.