Have you ever applied some sophisticated curves directly to a layer and then decided to change a bit? At least I have. And to do so, I had to do the same sophisticated curves once more time. Not very grattifying, is it? Well there is a solution.

Usually to invoke curves dialog I press Ctrl-M and then you change it and press OK. And as soon you clicked OK, you cannot change it? Wrong. Simply undo the last changes and press Ctrl-Alt-M, and the dialog with last curves will appear. Yes, Photoshop remembers the changes and allows you to apply or change them over and over, and not only in the current image - any document you open before you close the Photoshop.