a.hatena.js

// ==UserScript==
// @include http://a.hatena.ne.jp/*
// ==/UserScript==

(function() {

  function replaceLinks() {
    Array.prototype.forEach.call(
      document.querySelectorAll('a[href^="http://a.st-hatena.com/go?"]'), 
      function(a) {
        var num, frag = '';
        a.href = a.href
          .replace('http://a.st-hatena.com/go?', '')
          .replace(/\d{14}$/, function(n) {num = n; return ''})
          .replace(/#.*/, function(f) {frag = f; return ''});
        if (frag) {
          a.href += (a.href.indexOf('?') >= 0 ? '&' : '?') + num + frag;
        } else {
          a.href += '#' + num;
        }
      }
    );
  }

  var loaded = false;
  window.addEventListener('DOMContentLoaded', function(){loaded = true;}, false);

  var timer = setInterval(function() {
    replaceLinks();
    if (loaded) clearInterval(timer);
  }, 10);

}());