7 uses of USERNAME_MAX_LENGTH

install_configure_form in drupal-6.x/install.php
Form API array definition for site configuration.
user_admin_check_user in drupal-6.x/modules/user/user.admin.inc
user_edit_form in drupal-6.x/modules/user/user.module
user_login in drupal-6.x/modules/user/user.module
Form builder; the main user login form.
user_login_block in drupal-6.x/modules/user/user.module
user_pass in drupal-6.x/modules/user/user.pages.inc
Form builder; Request a password reset.
user_validate_name in drupal-6.x/modules/user/user.module
Verify the syntax of the given name.