One of the greatest drawbacks of AJAX is that it's simply too hard to code. The very fact that I can count the number of truly exploitative public AJAX applications on the fingers of one hand is an indication of that. What's needed are toolkits and platform support that can abstract some of the plumbing work and enable developers to focus on implementing the application itself.
I'm delighted therefore to see that the cat is out of the bag on Atlas, a series of components for ASP.NET that simplify the process of building AJAX applications. Atlas will include server-side controls that handle the async callback process, client-side web service access, a local cache, and client-side access via web service to the ASP.NET 2.0 profile and membership services. This latter capability could also be interesting in combination with an Avalon Express application, which could take advantage of some of these services to share the same back-end infrastructure as an ASP.NET application whilst integrating richer functionality.
More on Atlas at the PDC, of course!