ASP.NET ScriptManager control has a property LoadScriptsBeforeUI, when set to true, should load all AJAX framework scripts after the content of the page. But it does not effectively push down all scripts after the content. Some framework scripts, extender scripts and other scripts registered by Ajax Control Toolkit still load before the page content loads. The following screen taken from www.dropthings.com shows several script tags are still added at the beginning of <form> which forces them to download first before the page content is loaded and displayed on the page. Script tags pause rendering on several browsers especially in IE until the scripts download and execute. As a result, it gives user a slow loading impression as user stares at a white screen for some time until the scripts before the content download and execute completely. If browser could render the html before it downloads any script, user would see the page content immediately after visiting the site and not see a white screen. This will give user an impression that the website is blazingly fast (just like Google homepage) because user will ideally see the page content, if it's not too large, immediately after hitting the URL.