Drawing and annotating on separate layer
A feature that allows drawing with typical annotation-tool ( lines, arrows, boxes, text, freehand ) on top of any diagram would be very useful while developing and brainstorming/collaborating on a solution.
It could be implemented on a completely separate graphics layer with no added complexity in terms of connectivity to the diagram elements.
It would just need to scale along with the diagram layer.
Currently I use StarUML for generating the diagram, then export to pdf and use PDF-viewer to annotate the diagram. Would be fantastic if StarUML supported this directly.