Please see the tracker at SourceForge for the detailed list of bugs and feature requests.
Some really important ones to call out:
The UML Builder RPM won't install due to needing user_mode_linux, but I compile my own user_mode_linux so I don't have that.
You can make the UML Builder RPM install just by adding
umlbuilder won't run inside a UML session
It will, but you need to ensure that you are using a nesting UML inside the UML session. See this page for details.