Actually for those who are real digital painting artists there are a few very mature options (not Photoshop for sure) that can simulate almost perfectly the feeling (aside for the 3D brush icon, Corel Painter XI has all the features you've shown) of painting
but as you said that demands a lot o computational power. I'm professionally a developer butI have my art/design moments and would be nice to have a tool to fill this gap when designing a web site or even just sketching around (I love drawing, manga especially as you can see on my avatar).
It would be greate if you could integrate this tool to the next version of the Expression Studio 'cause it's one of then few things Adobe CS4 have that Expression don't, although Adobe tools are painfully dificult to master compared to Expression ones, Expression
does lack the presence of a raster image creating/editing tool.
I've gave up on understanting Flash interface in less than 2 hs but have being using Blend since 2 Beta 2 'cause it's way more easy to learn an powerfull to use and would be amazing to have something like that integrated to Expression to edit raster images