Well this certainly has been a passionate thread... just a few words about 'Adobe 3D' to respond to Brent's question. (Full disclosure: I am a technical evangelist at Adobe focused on PDF and the mfg industry).
eDrawings is a great tool and the differences really come down to scope and requirements of specific business processes.
The current feature set of Acrobat 3D version 8 really has been driven by 3D MBD requirements and for many of the use cases listed in this thread - specifically, how do you package all the relevant product data including a fully annotated 3D model or assembly and distribute that information efficiently (low/no cost viewer, small file size, appropriate interrogation tools, etc). The scope of this requirement is where you start to see the differences relative to many of the view and markup tools available on the market including eDrawings.
To be specific:
With PDF you can aggreagate multiple types of information into a single PDF document including 3D with MBD annotations, eDrawings just handles the 3D data and 2D drawings., I.e, no spec sheets, project plans, etc. that all has to be sent separately.
eDrawings stores all geometry as a surface tessellation; PDF v1.7 provides for precise B-Rep storage of geometry and subsequent extraction of that precise geometry to STEP, IGES, or Parasolid with Acrobat 3D for reuse by suppliers.
Also - PDF has built in security capabilities like digital certificates and signatures, and encryption that make it suitable for use cases that require approval as well as long term archiving.
There are some sample PDFs available here; the 'Transmission Order Form' near the bottom is probably the most comprehensive example and shows how 3D content can be leveraged as an information navigation system and integrated with PDF forms and digital signatures in the context of a compound document. These types of capabilities are not within the scope of products like eDrawings.