Today, I’ve found out a small trick accidentally. The trick is very useful because you can do more stuff with layer masks. You may already be familiar with the trick that you are able to activate/deactivate a layer mask by holding down the SHIFT-key and clicking on the layer mask-icon.
The new trick works similar: hold down the ALT-key on your keyboard and click the layer mask-icon in the layer palette to show/hide the alpha channel of the layer mask (black/white image).
This gives you great possibilities because you could even render clouds on your layer mask in order to create a complex mask effect. In Photoshop CS4, there are new layer mask features which allow you to do edit the layer mask separately (including its transparency). But so you have a “kind-of-CS4-feature” in your Photoshop CS/CS2/CS3.