Also, I've used Gimp a bunch and I've read the Gimp book from Apress and as far as I can tell there really is no such thing in Gimp as the non-destructive editing Nicole060 describes (assuming I understood the description correctly--that you can say first apply levels, then sharpen the image with unsharp mask, then go back and adjust the levels some more without the need to re-apply the unsharp mask--I don't think you can do this in Gimp.) So it's really a shame that the comment you replied to, which is truthful and presents a valid point of view, got downvoted into gray. And I'm saying this as a fan of Gimp who never used Photoshop.