The original exporter did not work for the latest Inkscape Version 0.91. As explained in http://wiki.inkscape.org/wiki/index.php/Notes_On_Units_Handling_in_Extensions_in_0.91 a reference in the source files had to be changed to get it working. find attached an updated version of the extension pack. Just unzip and copy to your local inkscape extension folder. NOTE: I observed that some times the conversion of units is done correctly only if the inkscape drawing is first exported by the standard inkscape DXF Exporte (R14) and after that once more by the OpenScad DXF Exporter. The standard DXF Exporter has a dialoge to set the units. Settings units to "mm" seem to influence output of the OpenScad DXF Exporter as well.