In the previous part I demonstrated how jQuery animations can add some jazz to your web forms. Now let's see one of the most important feature of jQuery that you will probably use in all data driven websites - accessing server data. In the previous articles you used jQuery methods such as $.get() to make a GET request to the server. More powerful feature, however, is to make AJAX calls to ASP.NET Web Services, Page Methods and WCF services. The $.ajax() method of jQuery allows you to access these services. In fact $.get() method you used earlier internally makes use of $.ajax() method but restricts itself only to GET requests. The $.ajax() method provides more control on how the services are called.

http://www.bipinjoshi.net/articles/479571df-7786-4c50-8db6-a798f195471a.aspx