I recently ordered two of Apple's photo albums using iPhoto. One of the books went through without a hitch, but with one of the books there were problems with the text and Apple canceled the order. I came to find out that even though I used the guidelines to line up the text, there is a bug in program. It seems some of the text become truncated and was cut out and would not have been published had Apple continued with the order.
However, there is a way to check that the text is lined up correctly before the order is sent to Apple. Proceed normally and assemble the book and just before ordering go to Finder. Select 'Go' from the Finder menu, then 'Go To Finder' and enter '/tmp' in the dialog box. In the resulting window, an iPhoto folder will appear, within that folder is the PDF of the book you just compiled. Open this file and you will be looking at what Apple is sent to print your book. From there, review the book for cut text, missing images, and look at the crop lines to view what will be cropped.
iPhoto4 Update: Although this hint works with iPhoto4, the location of the file has changed. While it's still in the /tmp folder, it's now more deeply buried. If you're the normal first admin user of the machine, you'll find it in /tmp -> 501 -> TemporaryItems -> iPhoto; if you're not the first user, then '501' will be replaced by another number, but the rest of the path will be the same.