If you do it right, using Ajax techniques can improve accessibility. Surprised? You shouldn't be. Ajax, like most techniques and technologies on the web are what you make of them.
That's why I asked Derek Featherstone to speak with me about his latest work. Derek is a world renown expert on web accessibility. As principle of Further Ahead, he also helps clients deploy sites that exploit the latest techniques. These two statements do not need to be at odds with each other!