Someone on InkscapeForum.com mentioned that DXF export had taken nearly an hour on a large file: http://www.inkscapeforum.com/viewtopic.php?f=18&t=674 . See that page for my reply explaining why the Python script is so slow, and how it can be made much faster. (Briefly: it's making what the Python Wiki calls "a very common and catastrophic mistake when building large strings".)
I'm attaching a patch to fix this.
A suitable test file can be found on OCAL: http://openclipart.org/media/files/johnny_automatic/4542 . I chose this one because it's large enough to show the problem, but small enough not to take an hour. With this test file, the current version of dxf_outlines.py takes over 6 minutes on my computer, but the patched version takes only 16 seconds.
Thanks for the patch, sas!
Hey Aaron, could you check this out and apply it if it passes muster?