Many users ask me how to manage multiple iPhoto Libraries. Usually, I tell them to download a script called iPhoto Librarian, which allows you to select which iPhoto library the application will use. Well, I just found out there's a way simpler (and built-in) solution. All you have to do is hold down the option key while launching iPhoto. A dialogue box will appear with the following options: Quit, Create Library... or Choose Library... The three options are self-explanatory. Compared to using iPhoto Librarian, which is a great app, btw, Option-launching iPhoto gives you a more automated way of managing multiple libraries.