There is actually an advantage to these books. Buy one of the Idiot guides, read it overnight, don't break the spine or open the attached CD. Take the book back the next day and swap (store credit) for a real book. The good thing is that they're a good way to find out what's important in the basics, but don't go any further.
You mean reading an Idiots or Dummies Guide does not make you an expert? At least you read something and have a little knowledge. I work with a whole group of people who have far less qualifications then that for the jobs they are in!
A guy at work recently played a joke on me since he knows I have almost all the books on Java that are worth having. He came up and said "I bet I have a book on JSPs that you don't have!" I lost $5 on the bet