gist_replace_title_with_filename.user.js

// ==UserScript==
// @name           gist: replace title with filename
// @namespace      http://d.hatena.ne.jp/youpy/
// @include        http://gist.github.com/*
// @include        https://gist.github.com/*
// @exclude        http://gist.github.com/gists
// @exclude        https://gist.github.com/gists
// @require        https://gist.github.com/3242.txt
// ==/UserScript==

(function() {
  var username = $X('id("owner")//a')[0].textContent;
  var filenames = $X('(//a|//span)[parent::div[@class="info"]]').map(
    function(span) {
      return span.textContent.replace(/ #$/,'');
    }
  );

  if(filenames.length) {
    document.title = document.title.
        replace(/^(gist: \d+)/,
                '$1 (' + filenames.join(', ') + ') by ' + username);
  }
})();