I couldn't find other mentions of this on the forums.  It's is not a big deal, but I figured I would let you know:

In a DataTemplate for a TemplatedNode, I tried using a Run in TextBlock. But when I clicked on the text with the intention of dragging to move the node around, an exception was thrown.  I easily got around the situation by using "
" in the Text property of the TextBlock instead of the using Run and LineBreak items.

This is what I tried in the DataTemplate:
<TextBlock>
    <Run Text="Hello" />
    <LineBreak />
    <Run Text="World" />
</TextBlock>

This is what fixed it:
<TextBlock Text="Hello&#10;World" />

It was a System.InvalidOperationException that came from DiagramPresenter with the message: 'System.Windows.Documents.Run' is not a Visual or Visual3D.

Fixed, thanks!