1. Graphic designer (silimlar to photoshop)
2. Interactive designer (similar to flash but more powerful but less portable)
3. Web Designer (More dreamweaver than frontpage)

Together someone could at last take on, the professional graphics tools monoply controlled and owned by Adobe.

Who is expression targeted at?

Microsoft in the past has create some entry level graphic apps, Photodraw 2000 (later merged into visio) and Digital image Editor but these both got low penetration. Expression on the other hand is aimed at high end pro designer market with more high end features and this microsoft jumping into the deep end.

The price of apps generally is big deciding factor in it usage, the Graphic designer (Acrylic) is currently running a free beta and i suspect once the Vista beta 2 is finalised and the XAML API becomes more solid, Interactive Designer (Sparkle) will also release a free beta. This desperately need to happen as currently the only stable XAML animation editor is available via http://www.mobiform.com/ but this is VS 2005 add-in and as such only aimed at developers not designers.

Graphic designers will be the only people cabable of fully untilising XAML/sparkles potential and finding its limits, or else it will be left dev's, who cant and shouldnt be deciding on UI design. Look to DA and VML as lessons from history where we had very impressive engines but dev's couldnt see it potential eg: http://www.geocities.com/sly_i/datest.htm. If you look at the code, it looks relatively simple but then look at the code cube.x file and you'll understand the barriers that dev's and designers were then confronted. XAML is definatly more simple for designers and dev to get to grips with and at stage i should hope so.

Should it be free?

I cant see graphics being a core MS focus and potential cash cow like say window, office, games or adverting but its DirectX underpinning if fully explored and untilised will allow these core products to be simply outstanding. Apple included X-Code (think VS 2005/Borland) free with the MacOS X CD, this i personally believe allowed MacOS X to get 15,000 new apps so quickly, by making new product development free and included and relatively simple.

For Vista , its needs a bold step like this, but not for coding but designing apps by giving it out for free. Or even just slimed down version of sparkle, sparkle lite*, free and included on the vista CD this would surely speed up the development and adoption of XAML/WPF app and maybe expression as a whole. But winfx 1.0  runtime will need to be a download for winxp to ensure it doesnt get sidelined until vista adoption increases.

* Hopefully something better than xamlpad or http://msdn.microsoft.com/archive/en-us/samples/internet/vml/vmlgenerator/default.asp