Ajax is one of the hottest buzz in today's web development world and Google and some other companies have used Ajax very wisely to improve his web applications and services. Every web developer is thinking about ajax. Ajax is a universal technique you can use it with any platform.
Microsoft has also built Ajax framework called Microsoft Asp.net Ajax formerly know as atlas. ASP.NET Ajax is very easy to user and simple to develop Ajax enabled applications.
I have found a great article which consider things a developer( who is developing Ajax enabled applications ) should know.
here is the link for that article.