"Donna Maurer (Donna Maurer)":http://maadmob.net/donna/blog/ have a nice article about "Usability for Rich Internet Applications (Usability for Rich Internet Applications)":http://digital-web.com/articles/usability_for_rich_internet_applications/ (via - "Digital Web Magazine (Digital Web Magazine)":http://digital-web.com/).

She list out the key features of typical RIA as;

* The user interacts directly with page elements (inline editing, drag-and-drop, panning a map)
* Part of a page is updated (instead of reloading)
* More detailed information is available on the same page (instead of on a new page)
* Feedback, confirmation and error messages are provided within the page

"Read the Full Article(Usability for Rich Internet Applications)":http://digital-web.com/articles/usability_for_rich_internet_applications/.