just for fun I tried Extensions>Render> Lasercut Jigsaw and got this message:

Traceback (most recent call last):

File "Lasercut-jigsaw.py", line 879, in <module>
e.affect()

File "C:\Program Files (x86)\Inkscape\share\extensions\inkex.py", line 268, in affect
self.effect()

File "Lasercut-jigsaw.py", line 798, in effect
docW = inkex.unittouu(self.document.getroot().get('width'))

AttributeError: 'module' object has no attribute 'unittouu'

I just imported a small jpg to experiment with, is there something else I need to do?

The extension might not have been updated for Inkscape 0.91 apparently: here's a solution (that I haven't tried): http://www.inkscapeforum.com/viewtopic.php?f=5&t=18620