I've was just in a session with several participants trying the collaboration functionality in Freewheel. Already it's useful. You can add any DWF file or publish directly from AutoCAD, Revit or Inventor.
Notice how you can sketch, highlight, add callouts and even apply Impression styles like above where I used Pen Wiggle.
The new navigation wheel (also seen in Autodesk Design Review) helps so you can navigate in both 2D and 3D. It is really user friendly.
If you create a session you can keep it active even though you close down your web browser. A day later someone can log in, add some comments and so on.
Of course there a some glitches here and there and features that you would like to see so just send the labs team an email and let them know. BTW. It is free! Give it a try.