The Autodesk Express Viewer is getting more and more robust. DWF is far more better than a PDF and is more designed specifically for your design data. In addition the DW6 format allows for benefits than PDF such as:
* Viewer Size
* Speed
* Smaller File Size
* Higher Resolution

More information on DWF http://www.autodesk.com/DWF

If you would like to participate in this beta, please feel free to enroll before the beta is completed.
http://betaprograms.autodesk.com/betaweb.htm

Cheers,
-Shaan