Quickly rating photos!
Rating photos in your iPhoto library is really useful because you can then specify that you only want to look at "four stars or more" or maybe "three stars or more" pictures. Rating the photos one by one in the "Information" box that is in the lower left corner of iPhoto is really long though. The quick way that I discovered is to double-click on the photo (it brings you to a preview mode, not the edit mode) and press anything from "Command - 0" to "Command - 5" depending on the rating you want. If you click on the "i" in the lower left corner before, you will get the information box and you'll then see the rating being added live.