Besides being able to crop graphics and photographs, Leopard has added more sophisticated color and sharpness adjustments (from the Tools menu, choose "Adjust Color"). And there is now a Lasso tool so you can be more specific about cropping and masking.
The annotation features have been greatly improved with useful new options. You can even create links on existing PDFs that jump to other pages in the same document or to web pages. I forgot to put this in the book, but in addition to sending a link to a URL, you can make the link open an email message ready to send: instead of typing a URL in the "Annotations" pane, type mailto: and then the email address (don't put a space after the colon).
And, of course, you can still copy text from a PDF as either editable text or as a graphic, then paste it into any other document.