In "Six Fresh Tips from iPod: the Missing Manual", you're likely to find at least one new tip that you hadn't previously known about. For me, it was the one about storing full-resolution photos on your iPod. Other tips include how to safely reset your iPod, loading songs from multiple computers onto a single iPod, and downloading iPod-ready videos from Google. Nice write-up and well worth a read.
Full disclosure: I also write for O'Reilly.