been testing artrage for a while now, and I like the fluidity of it.
but there are issues I as an professional artist can't stand.

One thing that would be really good, is to be able to customize the layout better. one problem is that all the white is bothering me, i would rather work in a grey enviroment, with as less color on panels as possible, just to eliminate that they affect the painting. and less framing on panels, everything that can save space is a good investment for thoose who want to have no distractions and use every inch of the screen.

So my points on this subject is:
1. I want to be able to set the color for panels and background to any black and white color, this would also add to the proffessional look of the program, for thoose pro's out there using this program.
2. if you're worried that an userface with more options would scare away grandma, why not do a advanced mode? so you could switch to advanced somewhere in the menu's.
3. I really like the color wheel, and that palettes are placed on the borders, but, the white 3d border and yellow buttons take down the impression.
4. brush preset? why not add that? I use the paint roller a lot, and the oils.
so, it would speed up my work in this program a lot not to change settings all the time, as i might use about 5 different settings of the same brush variant.
5. the brush-picker panel is not that good designed if you need to add more tools. having a list would be a lot easier, perhaps in a list at the bottom?

And never even think of taking away tablet support, why use a mouse in a program like this? i think many people that lke to paint on the computer gets a tablet sooner or later, mouse shouldn't be the first priority.

Another thing...
Color management
this is crucial to my working with graphical program, when I export to another program I want it to look the same, right now art rage psd get dull color when i export it because it's sRGB.
(I like that you got psd support, that makes it really interesting using artrage and photoshop in symbiosis, that works really well)
If I could set the colorspace in artrage I would be really happy (using adobeRGB mostly).

and! setting brush size in another way than % would be great, so you can get how big brushes you want.

And some cheering also, the brush engine is so fast! good work. the zoom works really great, but perhaps you would want to be able to use the Z zoom with the express strip on the intuos3.
the price for artrage is...cheap, if it would go up to the double for the advanced mode, there wouldn't be a problem for a pro buying it. but it's great you keep the prices down.