This will be double posted to the Ajax board as well, question if you wish to know about accessibility and use AJAX or just want to use AJAX but should know about accessibility issues.
- AJAX and Screenreaders: When Can it Work? - James Edwards aka Brothercake
- AJAX, Accessibility & Screen Readers - Ian Lloyd
- Accessibility of AJAX Applications - WebAIM
- Build Half a Product: Is Ajax accessible? At all? - By Joe Clark
- Usability tests of Basecamp with screen readers and other adaptive technology - by Joe Clark refference to the above article.
- Making Ajax Work with Screen Readers - Gez Lemon
- DOMScripting: Hijax - DOMScripting
- AJAX and Screenreaders: When Can it Work? - James Edwards for SitePoint