A friend uses SAI PaintTool for art (video demo). It's Japanese software, and what makes it special is that it uses vectors for the lines, and bitmaps for other stuff. (Normally "paint" apps use bitmaps, and "draw" apps use vectors.)
That's a really good idea, but it's Windows only, and it seems the program is not being updated anymore, and so on. So does anybody know a good paint app which uses vectors for the lines? Mac preferred, but I might get a Windose machine or install a simulator if I find a really good app.
I guess that while I do fine art, I don't do it in the naturalistic oil-painting tradition, but more in the modern acrylics tradition, more like comics or posters, lots of lines. So emulation of traditional media is not important to me.
I think Adobe Illustrator is quite powerful, but I think the interface sucks ashes, it always confuses the hell out of me.