[buro9]

OK, This version takes care of edits too:

  // HACK : START : ME
  global $post;
  if ('' == $post[username]) {
    global $reputation;
    if ('' == $reputation[username]) {
      global $pm;
      if ('' == $pm[fromusername]) {
        global $postinfo;
        if ('' == $postinfo[username]) {
          $meUsername = ''; // Can't determine username
        } else {
          $meUsername = $postinfo[username];
        }
      } else {
        $meUsername = $pm[fromusername];
      }
    } else {
      $meUsername = $reputation[username];
    }
  } else {
    $meUsername = $post[username];
  }
  $bbcode = preg_replace('#^/me (.*)$#im', "<span class=\"postAction\">*$meUsername \\1*</span>", $bbcode);
  // HACK : END : ME

Remember to strip my formatting

I think new replies are already dealt with by the $post one are they not?

I can't find a scenario in which it no longer works on mine.