The only problems I see with PDF VS DWF are:
1. DWF Viewer "VoloView" is available from Autodesk, but it is a HUGE download, however DWFs are very small in size.
2. PDF Viewer "Adobe" is readily available, in fact MOST people probably have it installed already AND it is a much smaller download than VoloView, however PDFs are generally much larger than DWFs
3. People not familiar with VoloView may not readily know how to download VoloView, but most operating systems can effectively find and download Adobe.
4. In DWF vs PDF Resolution, DWF is the winner hands down.