I often have several files open for which I only need JPGs, so I use "Save as" or else they will be PSDs. When I get around to closing them, Photoshop prompts "Save changes to the Adobe Photoshop document "image_name" before closing?" That gives the false impression that changes have been made since I actually did save the file using "Save as." So, just to be sure (did I forget?), I have to "Save as JPEG" again! Photoshop should prompt "JPEG saved, save as PSD?" when the file has already been saved in some format.