Here’s an interesting Topic for developers getting started off on Ajax: Design Patterns for Ajax Usability. A good article even for experienced developers on Ajax.

“AJAX holds a lot of promise for web usability, and the underlying technology has already delivered some stunning applications. But it’s no magic bullet. Careful design is always required, and it must be based specifically on the technology at hand. …
The point is to discover best practices by investigating how developers have successfully traded off conflicting design principles. AJAX is all about usability, so the patterns focus particularly on delivering usability in the face of constraints, most notably: user capabilities and expectations, bandwidth limits, the stateless nature of HTTP, the complexity of Javascript.“
Link : Software As She’s Developed - AJAX Patterns: Design Patterns for AJAX Usability