Matt Mason noticed the DWFx press release and its impact with Windows Vista and the XPS format. Matt also noticed in the presentations that Freewheel (http://www.dwfit.com) now supports 3D DWF files.
So now the biggest comment I hear why some use PDF instead of DWF is only because they have PDF installed. Now with DWFx, most Windows XP, 2003, and Vista machines will have the built-in ability to view 2D DWFx files with nothing to install. I understand the DWFx is also included in .NET 3.