[Reference]How to make a Gmail-like loading indicator with ASP.NET Ajax

At the moment I'm working on making a web application we just developed more user friendly and more appealing to the end users.

The application uses a few ASP.NET Ajax controls so I was pretty surprised when the customer sent me an email saying that he liked all the dynamic loading and the fact that he could reorder "things" using drag&drop and saving them without waiting the page to reload, but it took him a while to understand was going on. The first time he clicked the button, and since nothing happened, he thought that something was going wrong, so he kept clicking on the button, an yet nothing happening.

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http://codeclimber.net.nz/archive/2007/05/17/How-to-make-a-Gmail-like-loading-indicator-with-ASP.NET-Ajax.aspx