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/*
// @exclude        http://gist.github.com/gists
// ==/UserScript==

(function() {
  var $ = $ || unsafeWindow.$;
  var username = $('#owner a').text()
  var filenames = $.map($('span.code'), function(a){return a.textContent})

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