It looks like 3D PDF technology is starting to ‘wake up’. Another company, Intratech, plans to release a Revit 3D PDF export plugin in January 2012.
This will likely be in direct competition to the Tetra offering.
Another commercial option is SimLab Composer. From Revit, you export a FBX or DWG file, and then use SimLab Composer to turn the exported file into a 3D PDF.