[Tiberius]

I saw eflouret's technique, and thought that looks pretty good, so I followed his instructions and used that as a base to make a watercolour effect.

1. Follow the instructions in eflouret's post.
2. Duplicate the layer twice.
3. On the top layer, go to FILTER, BLUR, MOTION BLUR and set a motion blur at 90 degrees (so it's going up and down). The amount to use depends on the size of the image, but I used 20 pixels.
4. However, this leaves the eyes, mouth and nostrils blurred, so create a layer mask on the blurred layer and use a black brush with a low opacity to let some of the unblurred eyes, mouth and nostrils from the layer beneath to show through. Don't do it too much, otherwise the watercolour effect on't come across on the eyes, and it looks really freaky. Just use it to define the outlines of the eyes, mouth and nostrils a little. Don't worry about getting it right straight away, because you can come back and adjust it later.
5. Now, create a new layer that is on top of all the other layers and fill it with white.
6. Now create a layer mask on your white layer.
7. Select a brush that looks like a paintbrush (so not your standard round brush, but one with a bit of texture), set the opacity way down to about 10-15%, set the brush size to a fairly large brush (about 100 pixels works pretty well in this case) and start painting on the whaite layer's layermask in short downward strokes.Keep the brush strokes within the basic shapes though - for instance, I kept the strokes of the umbrella outside the strokes I used to show her face through. A bit of overlap is fine though. Don't worry about being too neat, and don't worry if you don't go all the way to the edges. It actually looks better if it's a bit messy.
8. Now, reduce your brush size a little and increase the opacity (i brought mine up to about 50%), and go over the subject and other areas that you want to define a little more. Then repeat the same process; short downward strokes, keeping confined to the shapes.
9. Keep going until you are happy.If you want, you can reduce the opacity of the blurred layer a bit to bring out the details a bit more.

And here's the result I got from this, bearing in mind I did a rushed job.