Add the ability for the user to click and drag out a region of the Mandelbrot set to zoom in on.
Existing images do not move if you resize the ImageSnarfer window. They either get clipped or the window gets a large expanse of white space, which looks strange. Make the window resize prettier, according your own definition of pretty.
The SnarfOperations stop loading when the window is resized or when a menu is being displayed. Why? (Hint: run loops.) Make the images continue loading even when the window is being resized.
NSOperationQueue can create new threads for non-concurrent operations if one of the currently running operations enters the kernel. You can work around this by explicitly calling -setMaxConcurrentOperationCount: on ...