Once you become more sophisticated and have a very large library of photos, you should probably invest $80 in Aperture. It has professional level photo editing capabilities and unlimited options when it comes to making books. I am an amateur photographer at best, but find that its intuitive editing tools make it easy to refine any picture.
Aperture also has an amazing organization and library management system which enables you to harness, sort and find all the pictures you need for any project. I was able to organize my over 25,000 photos within a few days and feel this is worth the price of the software alone. You can see in my library below that I typically sort by year and then event, but do pull out some specific categories such as sports, holidays, and various photo book projects. The built in search capabilities are very impressive.
It's pretty seamless to switch back and forth between Aperture and iPhoto as they share the single photo library and have the same book making facility. I find that I still use both programs depending on what I want to do. iPhoto is good for cards and photo picture books and Aperture is great for more sophisticated books that require more text and more customizable formats.