DPX's Shapebuilder tool can be used to paint with vector shapes. large soft semi transparent strokes can give a water colour wash effect, semi transparent strokes can also be overlaid and colours will mix. you can fill your strokes will fractal fills and give your painting a bit of texture, and you can even use the shape builder to paint in shadows and shading.
Here are two quick examples of what the shape builder can do. Has anyone else been experimenting along these lines? All are welcome to post their ideas, techniques and examples in this thread! Lets experiment together!