Add this as a reference if someone else want to use SketchFlow.
To illustrate geometries I use, Pen for polylines:
To get a sketchy look I change the Stroke by choosing BaseBorder-Sketch.
Rectangle-Sketch to fast draw polygons as rectangles :) otherwise it should be possible to use the Pen tool for this as well:
Circle-Sketch for points:
Here I change the background and border to BaseBorder-Sketch to get a filled point.
Resulting in something like this:
For icons on toolbars and other image resources I found a note on Import current UI into sketchflow about using Paint.Net to create sketchy looking images.
To do this open an image in Paint.Net and use Effects | Artistic | pencil Sketch...
Then add the images as background in buttons to create a toolbar or just add the image to the screen.
ArcGIS Silverlight/WPF Web APIs
I've also looked at the possibility's to use the ArcGIS Silverlight/WPF web APIs to do this but it felt like it's a bit complex to easily add concept to a prototype.
But if you want to add some background map. It can be done by adding the Map control that gets integrated in SketchFlow when installing the web-API:
Add layers by using the properties:
It's also possible to add a GraphicsLayer to add a Polyline using the XAML editor:
Well that my findings so far...