AJAX and ATLAS are two hot topics in the arena of web application development.
In this blog entry
, RickSP covers a talk he presented at Mix'06 on how to "Design a Better User Experience with AJAX and ATLAS", and in particular, six "lessons from the trenches". My take is that these should really be "Six pillars of AJAX application design".
The two sites he references on AJAX Design Patterns and AJAX (XMLHttpRequest) Usability are an excellent read too.