After reading Mark Pilgrim's article about the Q tag, I decided, "me too!" Except that it doesn't display correctly in Internet Explorer, I wrote a filter, first for WordPress, and now for Drupal, which takes <q>text</q> or <q cite="[url]">text</q> with just <span class="q">text</span>. In my articles, I still use the Q tag, in the hopes of one day running a script to make a ranked list of the URLs I've quoted over the years. Note that the escaping below is correct, and necessary for the description to appear correctly in administer » modules.

You'll need to save the module as quotable.module. It adds a filter called "Quotable" which you will have to enable for your input formats under administer » input formats.

/**
 * Implementation of hook_help().
 */
function quotable_help($section) {
  switch ($section) {
    case 'admin/modules#description': 
      return t('Adds a filter that replaces <q>text</q> or <q cite="http://example.com/">text</q> with <span class="q">text</span>');
      break;
  }
}

/**
 * Implementation of hook_filter().
 */
function quotable_filter($op, $delta = 0, $format = -1, $text = '') {
  switch ($op) {
    case 'list':
      return array(0 => t('Quotable filter'));
    case 'description':
      return t('Replaces the <q cite="[url]"> element with a <span class="q"> wrapper');
    case 'process':
      $replace = preg_replace("/<q[^>]*>(([^<]|<[^\/]|<\/[^q])*)<\/q>/", "<span class=\"q\">&ldquo;\$1&rdquo;</span>", $text);
      return $replace;
    default:
      return $text;
  }
}