Will Silverlight and AJAX replace ASP.NET?
It may seem like with all of these new technologies, that Silverlight and AJAX will replace ASP.NET as the way to render content over the browser. However, that is kind of a misnomer, because Silverlight and AJAX are technologies meant to enhance ASP.NET, rather than replace it. For instance, all of this is meant to work within the realm of ASP.NET pages, and using the same existing plumbing as was available before, but providing an extra layer over top of it all. In addition, the AJAX extensions provide some additional services that it uses to provide the services it does.
However, it's not meant to replace this. Silverlight is very handy tool to have, but in my personal opinion, its usage is to enhance ASP.NET applications, at least as of yet. With Silverlight 1.0 not supporting everything that is available in WPF, this can often be a drawback to implement complete functionality within Silverlight's capabilities. Although Silverlight 2.0 seemingly will support many more features, I believe that the industry has too much leveraged in ASP.NET applications. This means that most organizations may use Silverlight to add flash-like presentations, provide advertisements, or increase the attractiveness of the GUI, but it isn't going to replace the major portions of the application.
The AJAX Control Toolkit provides an arsenal of tools available that use the full AJAX features of the framework. As the toolkit develops, you will see more of these leveraged in the industry in applications, and may replace a lot of the standard .NET server control usages. However, most of the toolkit was meant to enhance the ASP.NET server controls, not replace them.
Of course, who knows what will come in the future...