ASP.NET AJAX is a framework for building a new generation of richer, more interactive, highly personalized cross-browser web applications. This new web development technology from Microsoft integrates cross-browser client script libraries with the ASP.NET 2.0 server-based development framework. In addition, ASP.NET AJAX offers you the same type of development platform for client-based web pages that ASP.NET offers for server-based pages. And because ASP.NET AJAX is an extension of ASP.NET, it is fully integrated with server-based services. ASP.NET AJAX makes it possible to easily take advantage of AJAX techniques on the web and enables you to create ASP.NET pages with a rich, responsive UI and server communication

It would be great to build applications today in XUL, but because it's not supported by 90% of the browsers out there, it's not considered a practical solution for most purposes (yet). However, AJAX programmers should keep an eye on technologies such as XAML and XUL. There is no doubt these technologies would make it easier to develop rich Internet applications, but they are in conflict with each other and don't have the same market penetration or momentum yet. AJAX is great for improving the usability of the Eeb applications that are there today. AJAX is not perfect, it's not "rocket science," and many developers and technology companies are trying better technologies for RIA all the time. The fact of the matter is that AJAX is here today and working, it's cross-browser and cross-platform, and both users and developers like what it can do. High profile AJAX applications like Google Maps have emerged as clear leaders in their field (who uses MapQuest anymore?). Likewise, leading Fortune 500 enterprises are using AJAX and are even contributing tools back to the community. In general, the industry has agreed on the underlying AJAX technologies and is using them. Renewed emphasis on rich Internet applications and a key advancement in browser technologies has made AJAX not simply a new tool in the developer's toolkit, but a phenomenon that is changing the way Web applications are written. Nobody can say for sure with what or when it will be replaced as the preferred platform for rich Internet applications, but many factors support a sustained AJAX presence over the next couple years.

Love it or hate it. The Web 2.0 movement is in full swing and turning the heads of programmers, VCs, marketers, and end users alike. This is definitely helping AJAX adoption for the time being; when the hype eventually dies down, it will be interesting to see what happens. AJAX interfaces are a key component of many Web 2.0 applications from BackPack to Google Maps. Likely the hype will help accelerate the adoption of AJAX and the usability benefits will keep it around. One of the key principles of Web 2.0 is using the Web as a platform for application development, instead of merely Web pages. Highly usable and interactive user interfaces are a key part of any application platform.

IE and Mozilla-based FireFox have the lion's share of the market and are arguably the easiest browsers on which to build AJAX Web applications, but now it's possible to build AJAX-based rich Internet applications that work on most modern Web browsers. This is an important reason why AJAX has become so popular. Although many developers were aware this was possibly years ago with Internet Explorer, it was overlooked because of the vendor lock-in factor. Thanks, Mozilla and FireFox

AJAX is based on open standards supported by many browsers and platforms; this means there's no fear of vendor lock-in. Most of the technologies that make up AJAX have been used extensively for years. These aren't hot, new, untested technologies that will only work most of the time. Browsers are a trusted application platform for most users and enterprises now; this wasn't the case five years ago. One of the turning points for AJAX was the Mozilla 1.0 release that FireFox is based on and supported the XML HTTP Request Object. This allowed the same asynchronous data transfer that had been possible in IE for years. That support and FireFox's rapid adoption really helped people understand that cross-browser rich Internet applications were possible.