Topic: How about breaking the line?
I saw such ability in other flowchart drawing porgrams... And I think, DiagramDesigner would only prosper if this feature would be in it.
Any line has three highlighted points - at the ends and in the middle. If user pull middle point - line automaticaly break into two independent lines (and two new middle points appears). Draging endpoint of some line to other endpoint of the same line should kills this line.