The Microsoft Learning folks have released a class that (at the time of this posting) you can take for free.  It is the: Developing Enhanced Web Experiences with Microsoft® ASP.NET AJAX Extensions class and it's about 2 hours in length.  If you have the time and the interest, take advantage of this training sooner than later, as you never know how long it will last.

Class Description:

In this 2-hour clinic you will learn about the rich functionality that ASP.NET AJAX Extensions provides for building highly responsive and enhanced web applications. In addition to learning about the different server and client components of ASP.NET AJAX, you will also learn how to build new ASP.NET AJAX applications and how to upgrade existing ASP.NET applications to take advantage of ASP.NET AJAX.
This clinic is appropriate for experienced .NET Web Developers and Software Architects who are looking to incorporate ASP.NET AJAX within their existing and future solutions.

Class Objectives:

At the end of the course, students will be able to:

• Compare and contrast traditional Web architecture with AJAX asynchronous post back operations.
• Describe the components of AJAX and the technologies it uses.
• Describe the purpose and benefits of using AJAX Extensions.
• Describe the relationship between AJAX Extensions and existing technologies.
• Describe possible uses for AJAX Extensions.

Here's the link to the class: Click here to access

~ Robert Shelton