DXF yuck!
segments , that is like mesh to NURBS. approximation to accuracy, segments of likes vs curves
i like the idea you are promotion Mark Thomas, alternatives, as we do need them
i say a better solution(s) are other tools:
i like Artweaver in place of PS ,
www.artweaver.de " IntelliCAD " " " Autocad ,
http://www.softsea.com/review/ProgeCAD-LT-2006.html (here is the free progecad 2006 LT) see Intellicad.org for all the other 'partners/products' ArchT, Architecturals etc
" Rhinoceros " " " " Illustrator/max/autocad/indesign (add Brazil , Maxwell, Vray, Fryrender, Indigo, Renderman, Flamingo, Penguin .. to render and Bongo to animate )
Intellicad being Open source with linux versions in Bricscad and it has full DWG compatibility in OpenDWG that Rhinoceros also uses and does as far as DWG compatibility with all current standard conventions
sure they are no revit archicad microstation or vectorworks. but there is tools like Archcut
http://en.wiki.mcneel.com/default.aspx/McNeel/ArchCut.html for Rhinoceros as well as all the traditional methods we know and use from the past till now plus way more flexibility over the control of your geometry, florkflow plus all the more advanced objs you can make.
Interoperability
i am still stuck in one area i like the Adobe Acrobat PDF print driver the best even thou i know tools like
http://PDFCreator.sf.net that are open source exist too.