只是个雏形，有时间慢慢改进，目前IE、FF、Opera都正常的！
HTML代码
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
*{font-size:12px; margin:0; padding:0;}
.cc{height:80px; width:960px; background:#CCC; margin:10px auto; padding:15px;}
.qq{float:left; width:80px; height:80px; font-size:64px; color:#F90; text-align:center;}
span{color:#F00;}
</style>
</head>
<body>
<div class="cc" style="height:400px;">这个是第一次加载的</div>
</body>
</html>
<script language="javascript" type="text/javascript">
<!--
function adddiv(){
}
var num = 0;
var max_px = 6000;
function pagestart(){
var h3 = document.body.scrollHeight;
var h1 = document.documentElement.scrollTop;
var h2 = document.documentElement.clientHeight;
var myDate = new Date();
var now = myDate.toLocaleString( );
if(h3 > max_px){
window.clearInterval(sid);
alert("已经滚到"+max_px+"了，不滚了！\nsid="+sid)
}
if((h1 + h2) < (h3 + 600) && (h1 + h2) > (h3 - 100)){
var txt = '<div class="cc"><div class="qq">'+num+'</div>这个是第<span>'+num+'</span>次加载的<br />加载时间：'+now+'<br />h1 = document.documentElement.scrollTop = <span>'+h1+'</span>（已经滚过去的高度）<br />h2 = document.documentElement.clientHeight = <span>'+h2+'</span>（可视区域高度）<br />h3 = document.body.scrollHeight = <span>'+h3+'</span>（body的高度）</div>';
document.body.innerHTML += txt + txt;
num ++;
}
}
var sid = window.setInterval(pagestart,500);
-->
</script>