I have devoted the past two weeks to fixing bugs in my viewBox based document unit implementation, deciding against implementing the object specific units I mentioned in my previous post. The most serious bug fixed was a bug that caused new objects to be defined in px with a transformation back to the document unit. A majority of the other bugs fixed were bugs in the transformations performed when changing the document unit from one unit to another. Just about everything is working properly now. With the Google Summer of Code drawing to close, I plan on fixing any remaining bugs I can find and merging my branch with the Inkscape trunk in the coming week.