First came 2D. Now you can view 2D and 3D DWF files on the web without installing any software. Since Project Freewheel is web based, you can view DWF files from any operating system such as Linux, Apple OSX, or even cell phones that have a web browser available.
Here is an example of a 3D DWF embedded in a blog posting. This is 3D DWF model from Autodesk Inventor - hosted by Shaan Hurley's Between the Lines blog. Go ahead and try the newly added Orbit command.
Check out http://www.freewheel.labs.autodesk.com. You can try uploading your own DWF files. Files can be 3D, 2D, or both.
For the latest information on Project Freewheel, see Scott Sheppard's It's Alive in the Lab blog.