This was provided with the RC1 announcement - http://www.dotnetnuke.com/Community/Blogs/tabid/825/EntryID/2010/Default.aspx.  

People often ask for "what's changed" with each release.  There are two levels of detail that we provide with each release.  1.  Release Notes  2.  Roadmap/Changelog.  

The intent of any release notes is not to duplicate what is in the Gemini Roadmap/Changelog but rather to give users a high level overview of features/bugs that have been included in a release which might warrant an upgrade.  Any release notes at best are just a user friendly account of the details provided in Gemini.   Release notes will be a running account of what will be in the final release.  As major new features are incorporated in successive Betas/RCs then they will be added to the release notes.  Release notes are a representation of the major highlights since the last official release.  If a user is wondering whether a specific bug has been corrected in a release, then they should consult the Roadmap/Changelog.

The RoadMap feature in Gemini shows those items which have been determined to be in scope for an upcoming official release.  Other bugs/features not on the roadmap may get incorporated into the release even though they were not in the original scope.  This allows us to respond to emergent events which occur after our initial scoping.  Once an official release (not a beta or RC) is packaged then the version will be moved from the Roadmap to the Changelog.

Future releases of DNN 5.x will also include the "what's new" menu item which wasn't quite working for this RC but which can be seen in DNN 4.9.0.  I will continue to create release notes for each beta/RC/official release and post those to the DotNetNuke Blog in conjunction with the release.