SO! Live. http://stackapps.com/q/1703/1165

so_live.user.js

// ==UserScript==
// @name          SO Live!
// @namespace     tag://badp/
// @description   Bring Live reputation requirement updates to the StackExchange™ EgoEmpowering HumanWorth™ counter.
// @include       http://stackoverflow.com/*
// @include       http://meta.stackoverflow.com/*
// @include       http://superuser.com/*
// @include       http://meta.superuser.com/*
// @include       http://serverfault.com/*
// @include       http://meta.serverfault.com/*
// @include       http://askubuntu.com/*
// @include       http://meta.askubuntu.com/*
// @include       http://answers.onstartups.com/*
// @include       http://meta.answers.onstartups.com/*
// @include       http://nothingtoinstall.com/*
// @include       http://meta.nothingtoinstall.com/*
// @include       http://seasonedadvice.com/*
// @include       http://meta.seasonedadvice.com/*
// @include       http://stackapps.com/*
// @include       http://*.stackexchange.com/*
// @exclude       http://chat.stackexchange.com/*
// @exclude       http://chat.*.stackexchange.com/*
// @exclude       http://api.*.stackexchange.com/*
// @exclude       http://odata.stackexchange.com/*
// @exclude       http://area51.stackexchange.com/*
// @exclude       http://*/reputation
// ==/UserScript==

//balpha <3
function with_plugin(url, callback) {
  var script = document.createElement("script");
  script.setAttribute("src", url);
  script.addEventListener("load", function () {
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.textContent = "(" + callback.toString() + ")(jQuery)";
    document.body.appendChild(script);
  }, false);
  document.body.appendChild(script);
}

with_plugin("http://soapi.info/code/js/stable/scripts/Soapi.js", SO_Live)

function SO_Live($){
  
  var api = Soapi.RouteFactory("api." + site);
  var last_update = now();

  function update_reputation_since(date){
  if(date === undefined)
    throw new Error("Please specify a date object.")
    
  last_update = now();
  api.UsersByIdReputation( { id: user_id,
                             fromdate: date 
                           } ).getResponse( function(data) {
                                                             
                                                             $.each(data.items, _parse_api_result);
                                                             window.console.debug("Updates received: " + data.items);
                                                             _schedule_next_update();
                                                            } );
  }

  function _schedule_next_update(){
    window.console.debug("Scheduling next update in 30 seconds, checking activity since " + last_update)
    setTimeout( function(){update_reputation_since(last_update) },
                30000)
  }
  
  _schedule_next_update();

}

//for the I can't believe I had to write this™ series
function now(){
  return new Date();
}

function to_num(val){
  var number = parseInt(val, 10);
  if( isNaN(number) )
    throw new Error(val + " is not a number");
  return number;
}

//http://www.mredkj.com/javascript/numberFormat.html
function add_commas(nStr)
{
  if(nStr > 999999) //this function breaks above one million.
    throw new Error("Sorry, you are too awesome for this mere function.");
  nStr += '';
  var x = nStr.split('.');
  var x1 = x[0];
  var x2 = x.length > 1 ? '.' + x[1] : '';
  var rgx = /(\d+)(\d{3})/;
  while (rgx.test(x1)) {
	  x1 = x1.replace(rgx, '$1' + ',' + '$2');
  }
  return x1 + x2;
}

//actual stuff

var site = window.location.hostname;
if(site !== "meta.stackoverflow.com") // metas do not count
  site = site.replace("meta.", ""); //get rep updates from parent instead.

var user_id = $("#hlinks-user a").first().attr("href").match(/[0-9]+/)[0];
       // get the URL address of the link to the user page; the sequence of digits is the user number, right? Right?
var rep_number_obj = $("#hlinks-user .reputation-score").first();

var debug_change = {
  positive_rep: 5000,
  negative_rep: 2000,
  title: "How do I move the paddle in Pong?",
  post_id: 42
};

function get_current_reputation(){
  return to_num(rep_number_obj.text().replace(",", ""));
}

function _change_rep_number_by(difference){
  var prev_rep = get_current_reputation();
  var new_rep = prev_rep + difference;
  rep_number_obj.text(add_commas(new_rep));
  return new_rep;
}

function lightweight_notify(show_this_message, duration){

/*
 0  0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
 |---'---'---|---'---'---|---'---'---'---'---'---'---'---|---'---'---|---'---'---|
 | fade out  | fade in   | display message               | fade out  | fade in   |
 | #hlinks   | message   |                               | message   | #hlinks   |
 |<---300--->|<---300--->|<-------------800------------->|<---300--->|<---300--->|
 |<---300--->|<------------------------1,400------------------------>|<---300--->|
 
*/
  
  if(duration === undefined){
    duration = 800
  }
  
  var fade_time = 300
  
  if( $(".lightweight_notify").length ) { //delay -- TODO: handle this better
    throw new Error("lightweight notifies overlap")
  }

  $("#hlinks")
    .fadeOut(fade_time)
    .delay(fade_time + duration + fade_time) //give the time for the message to appaear
    .fadeIn(fade_time);

  $("<span />")
    .css({'float': 'left',
          'text-align': 'right',
          'margin-right': 20,
          'width': '500px', //960-340=620-20=600 on SO, let's take less space for SE sites
          'overflow': 'hidden',
          'text-overflow': 'ellipsis',
          '-o-text-overflow': 'ellipsis',
          'white-space': 'nowrap',
          'font-weight': 'bold'
         })
    .addClass('hot transient-notification')
    .insertBefore("#hsearch")
    .hide()
    .delay(fade_time) //give the time for #links to fade out
    .fadeIn(fade_time)
    .delay(duration)
    .fadeOut(fade_time)
    [0] //get DOM object
    .innerHTML = show_this_message;
  setTimeout("$(\".transient-notification\").remove()", fade_time*3 + duration);
}

//http://stackoverflow.com/q/3953746/13992
function _schedule_rep_number_change(diff, step, number){
  setTimeout( function(){ _change_rep_number_by(diff) },
              4200 + step*25 + number*5000);
}

function _schedule_lightweight_notify(message, number){
  setTimeout( function(){ lightweight_notify(message, 3000)},
              number*5000
            )
}

function linkify(change){
  return $("<a/>").text(change.title)
                   .attr("href", "http://" + site + "/questions/" + change.post_id + "/-1") //give Community some love
                   [0] //get dom object
                   .outerHTML //cringe
}

function _parse_api_result(number, change){
  //lit up the envelope
  $(".envelope-off").toggleClass(".envelope-on")
                    .toggleClass(".envelope-off")
                    .attr("title", "You have new replies");
  
  var rep_net_change = change.positive_rep - change.negative_rep;
  var step = 1;
  
  var message = rep_net_change > 0 ? "Gained " : "Spent "
  message += Math.abs(rep_net_change)
  message += " reputation for "
  message += linkify(change)
  
  _schedule_lightweight_notify(message, number)
  
  while(rep_net_change){
    if(rep_net_change > 0)
      var diff = Math.ceil(rep_net_change / 10);
    else
      var diff = Math.floor(rep_net_change / 10);
    _schedule_rep_number_change(diff, step, number);
    rep_net_change -= diff;
    step++;
  }
}

How to try revision 6ab9d

1. Paste it in, get error SoApi is not defined
2. Paste it in again
3. update_reputation_since(new Date("2010-09-01 00:00:00Z"))

Following updates are actually functional.

How to try revision 7c5cb

1. Paste it in the javascript console.