Top Spammers Report

You might be interested in doing this (I have it in a custom module):

function mollom_menu{
  $items['block_ip/%'] = array(
    'title' => 'Block an IP address',
    'page callback' => 'mollom_block_ip',
    'page arguments' => array(1),
    'access arguments' => array('access statistics'),
    'type' => MENU_CALLBACK,
    );

  $items['admin/reports/top_spammers'] = array(
    'title' => 'Top Spammers',
    'description' => 'Spam count by IP address',
    'page callback' => 'mollom_top_spammers',
    'access arguments' => array('access statistics'),
    'type' => MENU_NORMAL_ITEM,
    );
  return $items;
}

/**
 * Count spams by IP.
 */
function mollom_top_spammers() {
  $rows_per_page = isset($_REQUEST['rows']) ? $_REQUEST['rows'] : variable_get('default_nodes_main', 10);
  $noyes = array(t('No'), t('Yes'));
  $dest = drupal_get_destination();
  $rows = array();
  $header = array(t('IP Address'), t('Count'), t('Blocked'));
  $title = t('Top @count Spam Addresses', array('@count' => $rows_per_page));
  drupal_set_title($title);

  $query = "SELECT hostname, COUNT(hostname) AS num "
    . "FROM {watchdog} "
    . "WHERE type='mollom' AND message LIKE 'Spam%' "
    . "GROUP BY hostname "
    . "ORDER BY num DESC";
 $result = db_query_range($query, 0, $rows_per_page);
  while ($row = db_fetch_object($result)) {
    $denied = drupal_is_denied('host', $row->hostname);
    $rows[] = array(
      $row->hostname,
      array('data' => number_format($row->num), 'align' => 'right'),
      array('data' => $noyes[$denied], 'align' => 'center'),
      array('data' => ($denied ? NULL : l(t('block'), "block_ip/$row->hostname", array('query' => $dest))), 'align' => 'center'),
      );
  }
  if (!$rows) {
    $rows[] = array(array('data' => t('None found.'), 'colspan' => '20'));
  }
  return "<h1 class=\"title\">$title</h1>" . theme('table', $header, $rows);
}

/**
 * Block an IP address.
 *
 * @param $ip - the IP address to block.
 * @return none.
 *
 * NOTE: a destination query parameter is required.
 */
function mollom_block_ip($ip) {
  db_query("INSERT INTO {access} (mask, type, status) VALUES ('%s', 'host', 0)", $ip);
  drupal_set_message(t('The access rule has been added.'));
  drupal_goto();
}