The Custom UI Editor has been updated so that it now works with the RTM version of Office 2007 AND the beta version of Office 2010.  It also incorporates a few usability improvements.

The main highlights of the tool are:

• adds support for dual parts where one is Office 2007 custom UI and the other is Office 2010 custom UI
• contains both the Office 2007 and Office 2010 custom schemas

The Custom UI editor can be found, along with a brief article about it, here