Thanks for your patience...
The Cheetah Beta site is now working: http://www-306.ibm.com/software/info/ids/cheetah/ - and so are the beta downloads: https://www14.software.ibm.com/webapp/iwm/web/preLogin.do?lang=en_US&source=swerpsw-idscob3.
Go on, try it. Also a new forum has been set up for Cheetah test run support: http://www-128.ibm.com/developerworks/forums/dw_forum.jsp?forum=1071&cat=19.
Check out Fernando Nunes' blog for a comprehensive summary of the many new features: http://informix-technology.blogspot.com/2007/02/cheetah-in-wild.html.