The only other thing - and I don't know how it compares to 3D pdf, but the 3D data can be extracted. I have been playing on and off with IMSI DoubleCAD and it (probably TurboCAD as well) actually imports dwf 3D models and allows the use/editing of those models. Of course accuracy is compromised when that is done.

>2D PDF being generally similar in functionality but kind of more widespread would probably come first before DWF.

That's kind of what I figured. I have been trying for years to get clients to switch to dwf the file sizes are almost half of the same pdf (2D vs. 2D). I don't have or know of any programs that do both 3D pdf and 3D dwf so I can't compare 3D files.