This control is really interesting but I having some problems with it...
Firstly, the labels bunch up when it begins showing hours. It becomes unreadable and performance takes a hit, reducing FPS when dragging the scroll bar. When I talk about the scroll bar I mean the bottom ResizableScrollBar named "Part_Scroll", not the center range selector "Part_RangePicker".
How to reproduce: Drag the bottom scroll bar so its size is reduced, thus zooming into the control and displaying smaller X values. Once it switches from days to hours on the bottom scroll bar, you will see many overlapping labels. This also occurs in the RangeNavigator sample contained in 22.214.171.124 dashboard WPF samples page.
Lack of customization options. No way to dynamically set what NavigatorIntervalType is currently being displayed on the top or bottom bars, no way to change date string formats (unless there's some style option I'm missing).
Not using a certain NavigatorIntervalType, i.e. Week, causes the top bar labels to be out of sync with the values. Can be reproduced in my sample the same way as the first issue. Drag the scroll bar until it becomes small and displays hours on the bottom bar. Then increase its size so it begins displaying days again. You will then notice the top bar will also display days, but they are out of sync, and are the wrong size (longer than 24 hours).