After vBulletin Roles Migration we can migrate the vBulletin users.

The following was added to the vbulletin_user.inc

    Database::addConnectionInfo('for_user_migration', 'default', array(
      'driver' => 'mysql',
      'database' => 'mysite_vbdatabase',
      'username' => 'mysite_d7user',
      'password' => 'myd7userpassword',
      'host' => 'localhost',
      'prefix' => 'vb_',
    ));


class vBulletinUserMigration extends vBulletinMigration {
  public function __construct() {
    parent::__construct();
    $this->description = t('Migrate vBulletin users');

    // Set the source table's primary key

    $this->map = new MigrateSQLMap(
      $this->machineName,
      array(
        'userid' => array(
          'type' => 'int',
          'unsigned' => TRUE,
          'not null' => TRUE,
          'description' => 'watw Unique user ID',
          'alias' => 'u',
        ),
      ),
      MigrateDestinationUser::getKeySchema(),
      'for_user_migration'
    );

    // Set the query to get the source object
    $query = Database::getConnection('default', 'for_user_migration')
      ->select('user', 'u')
      ->fields('u', array(
        'userid', 
        'usergroupid', 
        'membergroupids', 
        'displaygroupid', 
        'username', 
        'password', 
        'passworddate', 
        'email', 
        'styleid', 
        'parentemail', 
        'icq', 
        'aim', 
        'yahoo', 
        'msn', 
        'skype', 
        'showvbcode', 
        'showbirthday', 
        'usertitle', 
        'customtitle', 
        'joindate', 
        'daysprune', 
        'lastvisit', 
        'lastactivity', 
        'lastpost', 
        'posts', 
        'reputation', 
        'reputationlevelid', 
        'timezoneoffset', 
        'pmpopup', 
        'avatarid', 
        'avatarrevision', 
        'profilepicrevision', 
        'options', 
        'birthday', 
        'birthday_search', 
        'maxposts', 
        'startofweek', 
        'ipaddress', 
        'referrerid', 
        'languageid', 
        'emailstamp', 
        'threadedmode', 
        'autosubscribe', 
        'pmtotal', 
        'pmunread', 
        'salt', 
        'adminoptions', 
        'lastpostid', 
        'sigpicrevision', 
        'ipoints', 
        'infractions', 
        'warnings', 
        'infractiongroupids', 
        'infractiongroupid', 
        'profilevisits', 
        'friendcount', 
        'friendreqcount', 
        'vmunreadcount', 
        'vmmoderatedcount', 
        'socgroupinvitecount', 
        'socgroupreqcount', 
        'pcunreadcount', 
        'pcmoderatedcount', 
        'gmmoderatedcount'
      ));

    $count_query = Database::getConnection('default', 'for_user_migration')
                ->select('user', 'u');
    $count_query->addExpression('COUNT(userid)', 'cnt');

    $this->source = new MigrateSourceSQL($query, array(), $count_query, array('map_joinable' => FALSE));
    $this->destination = new MigrateDestinationUser();

    // Make the mappings
    $this->addFieldMapping('name', 'username')
           ->description('Map vBulletin username to Drupal username.');

    $this->addFieldMapping('mail', 'email')
           ->description('Import single vBulletin email field to both init and mail D7 fields');

    $this->addFieldMapping('created', 'joindate')
           ->description('Map vBulletin join date to Drupal user created date field.');

    $this->addFieldMapping('access', 'lastvisit');

    $this->addFieldMapping('roles', 'usergroupid')
         ->separator(',')
         ->sourceMigration('vBulletinRoles');

    $this->addFieldMapping('login', 'lastvisit');

    $this->addFieldMapping('init', 'email')
           ->description('Import single vBulletin email field to both init and mail D7 fields');

    $this->addFieldMapping('pathauto')
           ->description('Set to 0 for now');

    $this->addFieldMapping('status')
         ->description('Can we import the vBulletin frozen usergroup with id 8 to have a blocked status in D7')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0004);

    $this->addFieldMapping('pass')
         ->description('I think vBulletin 3x uses a salted MD5 and the old site also used a vBDrupal bridge so may be issues with D5 and D6 passwords to migrate to D7 but vBtoDrupal vbpassword module may help')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0005);

    $this->addFieldMapping('timezone')
         ->description('Not sure how to translate vBulletin timezoneoffset integers of + and - default or GMT timezone to D7 region timezones')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0006);

    $this->addFieldMapping('language')
         ->description('Not sure how to translate vBulletin languageid integer to D7 language field')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0006);

    $this->addFieldMapping('path')
         ->description('Need redirect from vBulletin user link to best for SEO user path alias in D7')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0007);

    $this->addFieldMapping('is_new')
         ->description('is_new is probably the best option but not sure')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0008);

    $this->addFieldMapping('birthday')
         ->description('vBulletin birthday format needs attention to import into D7')
         ->issueGroup(t('Implementor Issues'))
         ->issuePriority(MigrateFieldMapping::ISSUE_PRIORITY_MEDIUM)
         ->issueNumber(0009);

    // Unmapped source fields
    $this->addUnmigratedSources(array(
        'userid', 
        'usergroupid', 
        'membergroupids', 
        'displaygroupid', 
        'username', 
        'password', 
        'passworddate', 
        'email', 
        'styleid', 
        'parentemail', 
        'icq', 
        'aim', 
        'yahoo', 
        'msn', 
        'skype', 
        'showvbcode', 
        'showbirthday', 
        'usertitle', 
        'customtitle', 
        'joindate', 
        'daysprune', 
        'lastactivity', 
        'lastpost', 
        'posts', 
        'reputation', 
        'reputationlevelid', 
        'timezoneoffset', 
        'pmpopup', 
        'avatarid', 
        'avatarrevision', 
        'profilepicrevision', 
        'options', 
        'birthday_search', 
        'maxposts', 
        'startofweek', 
        'ipaddress', 
        'referrerid', 
        'languageid', 
        'emailstamp', 
        'threadedmode', 
        'autosubscribe', 
        'pmtotal', 
        'pmunread', 
        'salt', 
        'adminoptions', 
        'lastpostid', 
        'sigpicrevision', 
        'ipoints', 
        'infractions', 
        'warnings', 
        'infractiongroupids', 
        'infractiongroupid', 
        'profilevisits', 
        'friendcount', 
        'friendreqcount', 
        'vmunreadcount', 
        'vmmoderatedcount', 
        'socgroupinvitecount', 
        'socgroupreqcount', 
        'pcunreadcount', 
        'pcmoderatedcount', 
        'gmmoderatedcount'
      ));

    // Unmapped destination fields

    $this->addFieldMapping('signature') ->description(t('vBulletin long text signature to be replaced with one text and one link field in D7'))
           ->issueGroup(t('DNM'));
    $this->addFieldMapping('signature_format') ->description(t('Will be set manually'))
           ->issueGroup(t('DNM'));
    $this->addFieldMapping('picture') ->description(t('Will be reset in D7 to create new size and image types with imagecache'))
           ->issueGroup(t('DNM'));
    $this->addFieldMapping('field_migrate_example_gender') ->description(t('Not used in vBulletin but might be a new field in D7'))
           ->issueGroup(t('DNM'));
    $this->addFieldMapping('theme') ->description(t('Not used in vBulletin and themes will be different in D7'))
           ->issueGroup(t('DNM'));
    $this->addFieldMapping('field_signature_link') ->description(t('vBulletin long text signature to be replaced with one text and one link field in D7'))
           ->issueGroup(t('DNM'));
  }
}

As with vBulletin Roles Migration, the above includes a long list of fields that aren't need in my D7 site so they won't be migrated with ->issueGroup(t('DNM'));

There are probably also many fields that might not be in your own vBulletin setup, depending on any addons/plugins that you might have installed in vB