Here's a real time-saver. Save Image in Folder is a Firefox extension that lets you define common destinations for images you save from the web and execute a save operation with a right click (or control click on the Mac). You get to bypass the Save As dialog and, in the preferences, can even choose to use the browser cache rather the download history to store your image download actions. The add-in does work on both Windows and the Mac but the preferences are clearly PC-oriented.
Hat tip to Ryan Sullivan at Download Squad.