ideas from a discussion with wind-rider on #koffice:

The space navigator is very good for just navigating around in your
document (e.g. panning and zooming). But we also want to have support
for it inside the tools so we can for instance scale, move and rotate shapes, 
change the size of a brush, etc.
So we have to decide based on the actual working context where to
send the device events so that the right things happens.
Thats means if the user is currently working on a specific aspect of
the document, we should not pan/zoom the document by accident. This can
be achieved by using a keyboard modifier or a device button to switch 
between document and tool context.
Another problem is that the space navigator reports both position and
rotation changes in a single event. It would maybe be better to check the
most significant part of the event and only use that for the action to be
carried out. An example for tha twould probably be the default tool where 
we can rotate, scale and move the currently selected shapes. We certainly
don't want to rotate, scale and move at the same time. So we have to decide
which action we want to carry out. Hopefully we can decide that based on 
the position/rotation values. If that is not enough we have to use other
means to switch between those actions.
