I just came back from an all-day Silverlight workshop that I gave at one of my customer's offices for about 25 people. I got some great confirmation about the designer-developer workflow that we are proposing with the Expression Studio. One of the more enthusiastic participants in the training was an interaction designer. She was the only one that came with a Mac notebook; everyone else had windows notebooks. She promptly launched Expression Studio in Vista from Parallels (the system that lets you run windows on a Mac). She definitely wasn't about to give up her Mac for a Windows notebook but she really understood what it means to have the graphic designer create geometry and graphics that were used directly by the interaction designer (her) and handed off to the developer to hook up the application logic. It meant that she could confidently create designs that she knew were going to be implemented. This design fidelity - the ability for her design intent to be carried out in the final software product is what she was excited about.
This reminded me of one of the main issues that prompted me to go into software instead of architecture after getting my professional degree in architecture: the problem was the in order for a three-dimensional design to be created in three dimensions, it needed to be abstracted into paper (blueprints). Going from 3- to 2- to 3- dimensions is inefficient, inexact, and therefore problematic. But that process is a standard practice all over the world for getting buildings built. One architect, Frank Gehry found a way around the 3-2-3 problem by keeping the building model digital from design to construction. That enabled the kinds of designs like the Bilbao Guggenheim museum.
With the Expression Studio, an all-digital workflow is possible. What kinds of amazing designs will we start to see coming from designers using that tool set? Who will be the Frank Gehry of interaction design? Amaze me!