I have long felt that desktop RP was to 3D product design as desktop laser printing was to 2D graphics design. Like graphics design, 3D product design would only really take off when you could print a proof at your desk.
Sure, 3D WYSIWYG is also a key part of the solution, but we are there now. With all the new near real time renderers it is nearly impossible to tell a rendering from a photo.
One of the last big barriers to an explosion in 3D design has been affordable desktop 3D printing. The new uPrint Personal 3D Printer from Dimension breaks that barrier.
Of course, as soon as you finish setting up your uPrint Printer, you will be able to print directly to it from Rhino.