I've heard this question several times in the past few months and the answer is - an astounding - not even close. In fact, I would say that ASP.NET AJAX is going to enjoy a long and fruitfull life as a development tool for ASP.NET developers over the next three to five years at least, probably even more (though it may morph into something else during that time). However, this question - as to whether all the new client-side visual tools like Silverlight - is the end of ASP.NET AJAX is a fairly decent one given that, still, not a whole lot of people fully understand the depth of ASP.NET AJAX. Let's take a brief look.

First, ASP.NET AJAX is not only about AJAX; it's a full, complete, end-to-end framework for developers who wish to (or are forced to) dive into advanced client-side scripting. Quite literally thousands of controls are floating around in the world today that require the use of JavasScript - and millions upon millions of websites are leveraging it for reasons of client-side richness and control. What ASP.NET AJAX gives to the JavaScript (ECMA Script) developer is as close to an object-oriented, .NET'ish programming platform as you can get - so the need to write platform agnostic logic is either completely removed or mostly removed. For the millions of developers in the world right now who use JavaScript in their controls and web applications, development tools like Silverlight will not help.

Second, Silverlight is - like Flash - more of a user-interface platform all in itself. Like Flash, it will require the download of necessary bits to the client machine, and once there, will require a compliant browser to operate within. You will be able to create compelling interfaces, no doubt, but it's focus is always going to be angled towards the designer; the guys who think in the world of "flash'yness" (pardon the expression). A highly effecient, intuitive intranet or CRM solution, on the other hand, will probably not be written, ever, in a development framework like Flash or Silverlight - the same goes for an eCommerce webstore or a highly dynamic news site. These more business-oriented solutions will benefit greatly from the nature and flexibility of markup within the browser; and therefore find great benefit in the asynchronous attributes offered through ASP.NET AJAX. It would certainly be interesting if all the web pages out there looked like a high-end Silverlight presentation, but realistically, that wouldn't be practical at all to developer or maintain.

Third, ASP.NET AJAX is undergoing great advancements through the community - which shows a high focus on it as an important aspect of ASP.NET development. The open source community is contributing a great amount to the control toolkit, and this shows no sign of stopping or even slowing down.

And finally, and most importantly, Silverlight, Flash or what-have-you is not (nor probably ever will be) a natural environment to build products and solutions in for the ASP.NET, data-driven website developer. We have been raised under the notion of markup and are trained with that in mind, our websites are built around it, and the end-user expects it; the idea of removing or lessening the effects of this trend would be insane.

So, in summary, I see Silverlight being good for things like this:

• Kiosks,
  
• Company main or "splash" pages,
• Games,
  
• Presentations

...the kinds of sites where a designer would be involved mostly. And I see ASP.NET AJAX coming into play with:

• Intranets,
  
• Customer Portals,
  
• eCommerce sites
• Highly database backed or data-driven sites (like www.live.com)

...the kinds of things where a developer would be involved mostly.

Basically, there is no way ASP.NET AJAX is dead or nearing death. End of story.