A lot of times I masked out figures, because I wanted to blur the background. And then used a gradient to get a non-linear depth of field. If you starting doing this, inspired by this thread, I have two nice tips, learned it the hard way: First, if you end up with at least two layers and want to blur the background, some kind of halo will surround the masked figure (because it is also there). Before you blur, crop the masked item in the background layer with the clone tool. The effect will be much better. Second, If you use an alpha chanel or a gradient, do not try to blur your background in one pass, do it a lot of times, with a small value. Areas that are selected for 50% (because of a corresponding grayscale value) look 'ghosted' i.e. half of it is sharp, half of it blurred. With more passes this effect becomes less.