Autodesk web site now offers the DWF markup application, Design Review 2007 for free. Before you (or rather your partner) had to buy it for about 220 €.
This unlocks new ways of communication in the review cycle. Of course I prefer to receive the comments and markups in an electronic form to read directly into Inventor or AutoCAD but I could hardly imagine forcing the customer to buy a piece of software for this. Now it will be much simple.
Plus, the customer can measure the model or drawing in the DWF file. It was not possible in the DWF Viewer and not even in the DWG Viewer.
The Design Review web is www.autodesk.com/designreview