While I do not agree with 100% of this book and don't particularly enjoy the writing style of it, I generally like and agree with the information in it. The main points in this book include: promoting full feedings instead of snacking, frequent daytime feedings and awake periods (with the EWS cycle) to help baby distinguish day from night, teaching a baby to fall asleep on his own and the importance of sleep to both a baby and his parents.
The thing you need to be careful about while implementing the strategies in this book is to not become too obsessed about doing everything perfect, realize that every baby is different and don't be too strict with your routine. This method of parenting will work better for some babies than it will for others. Babywise kind of makes you think that your baby will follow the "routine" or "schedule" exactly but that is definitely not the case. There are going to be ups and downs along the way.
Just in case you're wondering, I did use the scheduling principles in Babywise (which were pretty much the same as the baby whisperer) and successfully nursed all my children past a year. I wanted to point this out since I am sick and tired of all the remarks that babies will be malnourished on Babywise. That is not true. If you are following the Babywise principles correctly which tell you to feed baby when he is hungry and to monitor weight and output, you should be fine.
Here is a great article about Babywise myths. There are a bunch of other "wise" books out there to help you with every stage of development. See "wise" books here.
Many people who like Babywise also really like The Baby Whisperer Solves All Your Problems. This book is similar to Babywise but doesn't agree with ever letting your child cry by himself which Babywise agrees with to an extent. Terrific Toddlers by Mel Hayde is also a great series that goes along well with Babywise.