With 1GB of RAM I thought I was safe, but no. I continued cloning a small area of a picture and everything froze, for ages. I've increased the RAM available to PS, but have discovered that working in 'Adjustment Layers' is far more beneficial in terms of reduced demands on computing power. I also read today about a useful shortcut. When you want to save your work but keep all your layers intact, create a new blank layer at the top of the stack. Hit, Shift + Ctrl + Alt + E This will flatten all your layers upwards, whilst leaving all the individual layers intact.