I bought PaintStorm and migrated from Photoshop, loving it so far!
I am using a dual monitor setup, painting on wacom cintiq and a large preview monitor above.
It would be great to be able to preview the current canvas in a separate floating window (without any ui, just zoom + pan + fullscreen), so I can have a clean view of my work, similar to Photoshop's Window > Arrange > New Window for Filename.
The second feature I would like to suggest is adding image drag and drop support into the mixer and reference panels, so you can just drag pictures from your desktop into the mixer or reference windows.
Thanks!
My most recent painting:

http://upheaver.com/projects/ax5ak