There have been lots of people writing about ajax recently, and more importantly about ajax accessibility.
Our content management system (CMS) has a caching functionality to speed up the delivery of pages, and while it clears the cache when you change any content, there can be a time where you want to force a refresh. Below is the HTML for the clear cache link.
<a onclick="ClearCache(); return false;" href="clearcache/"> Clear page cache </a>
Note that there is a `return false;` after the function call, this effectively cancels the click on the link, stopping the browser from navigating to the clearcache page. An important thing to note is that while the user experience is different in the two cases, they are both perfectly usable. It will even work in a text-only browser, such as Lynx.
You could also go the gmail route, and have two totally separate interfaces, one for modern browsers that support ajax, and another plain HTML interface for older browsers, however this is a lot more work, to support (usually) a small minority of users.