Flash Accessibility and Usability - Jakob Nielsen's summary of the Nielsen Norman Group's 2002 report on Flash accessibility describes five issues related to Flash and Usability.
Google Code: swfobject - Home of swfobject-- a standards friendly way of making Flash content accessible to browsers without Flash installed, including screen readers and primitive mobile browsers.
Making Flash Accessible - Outlines the problem of Flash Accessibility as it relates to Web Usability. Contains best practices, tools and links.