I was asked in an email from a blog reader "with the free DWF Writer printer driver, why do I still post PDF documents".
The answer is quite simple. While DWF is awesome and lightweight, it was designed specifically for CAD vector data. PDF is great at text documents, but it is absolutely bloated and inaccurate with CAD vector data. So when I post word documents I use PDF and when posting CAD vector design documents use DWF.
It is the longtime proven statement and rule of thumb to use the best tool for the intended purpose or output. There is no one size fits all format and perhaps that will change in the future. but right now DWF for CAD and PDF for text documents. The one downside to using PDF text documents online is the delays while the Adobe Acrobat reader takes all of your system resources and memory and almost locks your system up while trying to open the PDF document. It would be nicer to have a text document format able to be embedded in the web page like Flash and Macromedia with the Flash Paper can do that, but not CAD vector data.
The Graphical User Interface (GUI) is geared differently between Adobe Acrobat and the free Autodesk DWF Viewer. While Acrobat is set for serial document reading top to bottom scrolling the Autodesk DWF viewer is view based and allows panning zooming and 3D rotation when viewing 3D DWF files. So you have one geared towards small paper documents and one geared and designed for CAD layouts and data. Each are specific to what they were designed for one for text and one for CAD.
Choosing an electronic format for your CAD data just because the secretary has a viewer installed for PDF is not a solid foundation or the best reason IMHO. Your dentist would hopefully not choose to use his home drill to work on your teeth, as he would choose a dental drill specific to what he is doing and working on.