If you are doing any web development and have or will be implementing AJAX, you should check out the AJAX Patterns site for some good guidance. This Wiki site has a lot of great content and resources about AJAX, here is an excerpt from the site:
There are 70+ Ajax patterns here, most linking to the original draft version for the design patterns book. Foundational Technology Patterns are lower-level patterns and a suitable introduction for people learning Ajax for the first time. Programming Patterns explain how these components are combined in a maintainable, performant, manner. Functionality and Usability Patterns guide on user-interface and usability concepts. Development Process Patterns look at typical developer activities like testing and debugging.
P.S. - I found this site via July 2007 MSDN Magazine article, Cutting Edge: Context-Sensitive Feedback with AJAX by Dino Esposito.