WOW, think I just completed the Photobook for Mom.

[Kramerica]

If you are still using iPhoto 5, you need to do this before sending:

download free app called Pref Setter
quit iPhoto
run Pref Setter
search for iPhoto
this will show you the iPhoto plist settings
change
BookTargetImageDPI
BookTargetMediumImageDPI

to 300 instead of 150

Save.
Relaunch iPhoto.

This will make your photobooks print at 300dpi instead of 150 dpi which is the default in iPhoto 5.