I am expecting DC2 and while I think my expectations this time round will be more realistic someone has recommended this book to me as an aid to understanding the baby's emotional development, what's normal, how they might act etc.
I'm finding it great to have. It prepares you for what's coming and gives you ideas on games and toys that are useful after each 'leap'. What it doesn't do, and it states it right at the beginning, is give you parenting advice. For example it doesn't tell you if it's good or bad to teach your 20 week old kid to 'be patient'.
Defenitely worth shelling out for it though. You can probably get used copies off of Amazong.