I returned to swimming 8 months ago after a long break, and wanted to improve my front crawl technique, so bought Terry Laughlin's "Total Immersion". I've practiced almost daily and this book has definitely helped quite a bit.
There are 3 main techniques explained here which are key to swimming front crawl well; they are : balancing your body correctly, swimming long ie. with your arm extended and swimming on your side. Why these techniques improve your front crawl swimming is explained very well. Indeed the whole book is very readable and quite entertaining.
Step by step drills are given in chapter 8, to teach you how to progress to the complete stroke, which you may or may not want to follow. I personally didn't, but kept reading over the chapter to compare it to what I was doing in the pool. The book also recommends buying the accompanying DVD for the book. I didn't do this either as I found plenty of related Total Immersion video clips on the Internet.
Overall then, I found the book enjoyable and useful for improving my stroke. My only criticism is that there is very little about correct breathing in front crawl, which is actually quite important to get your stroke right. But again, there is plenty on that aspect of swimming on the Internet, so it isn't really a problem.
The only other thing I'd like to point out is that while the Total Immersion method is very well explained, and clearly works, there is a noticeable difference between it and competitive front crawl swimming. Watch some videos online of say Michael Phelps or Ian Thorpe and it'll be obvious that their arm stroke is different ie. the arm does not sink after entry. So, Total Immersion is not for speed. It is designed to teach relaxed, efficient swimming which is useful for say long distance swimming.
To sum up then, if you want to improve your swimming, I would definitely recommend this book. But at some point I think you will want to seek out other sources too eg. swimming websites online, to get a full overview of the front crawl stroke.