I think you can learn useful information from a self-help book, but I have doubts about their life-changing effects. It's important to keep in mind that not everyone has as much common sense as you! The information provided in "7 Habits of Highly Effective People" or whatever is probably hot hot new info to some people, but most of us could have already told them all of those hints. I don't think the books are completely useless though- I can always stand to improve
