Adds a "total rep today" number in the top bar for all StackExchange sites - Only works in Chrome, only makes a request every 30 min or when your total rep changes.

SODailyRep.user.js

// ==UserScript==
// @name           SO Daily Reputation
// @namespace      soRepDaily
// @description    Shows reputation for the current day.
// @include        http://stackoverflow.com/*
// @include        http://serverfault.com/*
// @include        http://superuser.com/*
// @include        http://meta.stackoverflow.com/*
// @include        http://*.stackexchange.com/*
// ==/UserScript==
(function(){
  var ro = JSON.parse(localStorage.getItem("CurRep")), 
      hlu = document.getElementById("hlinks-user"),
      s = document.createElement('span'), is = s.cloneNode();
  s.className = 'reputation-score';
  s.id = 'current-rep-top';
  is.className = 'bounty-indicator-tab';
  is.innerHTML = ro && ro.rep || "Fetching...";
  s.appendChild(is);
  hlu.insertBefore(s, hlu.childNodes[0]);
  
  function with_jquery(f) {
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.textContent = "(" + f.toString() + ")(jQuery)";
    document.body.appendChild(script);
  }
  with_jquery(function() {
    $(function(){
      if(!$("#topbar a[href^='/users/logout']:first").length) return;
      
      function leftPad(num) { 
        return (num < 10) ? '0' + num : num; 
      }
      
      var today = new Date(),
          UTCtoday = today.getUTCFullYear() + '-' + leftPad(today.getUTCMonth()+1) + '-' + leftPad(today.getUTCDate()),
          url = ($("#topbar a[href^='/users/recent/']:first").attr('href').match(/^[^?]+/))[0] + '?StartDate=' + UTCtoday + '&EndDate=' + UTCtoday,
          repNode = $('#current-rep-top'),
          pageRep = $("#hlinks-user .reputation-score").text(),
          ro = JSON.parse(localStorage.getItem("CurRep"));
          
      repNode.wrapInner($('<a />', { href: url + '&tab=reputation#tab-top' }))
      .attr('title', "Today's reputation so far, Ctrl+Click to force a refresh...otherwise it'll happen whenever your rep changes.")
      .bind({ 
        reload: function() { 
          $(this).load(url + " #tabs a[href^='/users/recent/'][href*='tab=reputation']:first" , function() {
            $(this).find('a').html($(this).find('.bounty-indicator-tab').add($('<span class="bounty-indicator-tab">0</span>')).eq(0));
            $("#hlinks-user").prepend(this);
            localStorage.setItem("CurRep", JSON.stringify({rep: $(this).text() || "0", day: UTCtoday, pageRep: pageRep }));        
          }); 
        },
        click: function(e) {
          if(!e.ctrlKey) return;
          $(this).find('.bounty-indicator-tab').text('Fething...').end().trigger('reload');
          e.preventDefault();
        }
      });
      
      if(pageRep != ro.pageRep || UTCtoday != ro.day) repNode.trigger('reload');
    });
  });
})();