We recently finished up another product development milestone, and at the end of it had a day-long bug-bash to find bugs in the product. Arturo and I teamed up and came with the simple "application" above done 100% using the Expression tools (and of course, VS for some coding purposes). Arturo came up with the concept and the visuals in Graphic Designer. I then made the application come to "life" using Interactive Designer.
We have been listening to your feedback, and we have been working hard on fixing the issues. You will be glad to hear that each of the contents of the tab items (the messenger buddy list, the FreeCell game, and some stock information) is its own "scene" (UserControls for those who care) that has been designed independent of each other (they share some resources like brushes) and has been put together in Interactive Designer. Hopefully, the days of massive XAML files are now gone!
I will post the source for this sample as soon as the new build of Expression Interactive Designer (and more importantly, a new version of WinFX run-time components) becomes available. Unfortunately, I don't have any release date information...