Alistair, I'm just posting "on the fly" right now so I've not the time to go into detail untill saturday or Sunday night if it is needed.
Here is a picture I made with actions using a simple shape to begin with. The shape was very much like the Nike logo, you know the shape that looks like a stylised tick.
Mandlebrotted Abstract
Here is the .RAR (ed) .PSD so you can get an idea of the steps I took.
Abstract .PSD Take note that it is about 6 MB in size.
Action Central is a good site to look at to give you a good idea of the possibilities using actions.
Tao