I'm not generally a fan of add-ons to the operating system or browser (it makes it confusing when switching from computer-to-computer), however one exception is the tool "CreateBooklet". It's simple, but brilliant, and I've used it extensively. Basically, it adds a menu option to the PDF dropdown box (when you print from any application on a Mac) to create a booklet automatically (in PDF) from whatever you are working on. Works perfectly and it is free. Visit their site and get it here.