The problem with books of this sort is that they're generally obsolete almost before they get published. The Six-Figure Second Income is a bit of an exception. It's actually a pretty solid book, filled with sound advice on general internet business practices and copywriting techniques. It would be an excellent book for a beginner, but even an old hand at internet marketing could pick up a pointer or too. Of course, it's a fairly new book -- it was only published in 2010. Still, I suspect it will stand the test of time.
Amazon Reviewers generally agree with me. They've given the book an average of 4.0 stars (out of a possible 5), with a total of 60 reviews.