I have both the 2nd and 3rd editions. The 3rd edition has color illustrations rather than B&W, and a third author is added. The preface says that was designed to give it a fresher look. The chapter on Extremes has specifics on lighting to make sure the shadows and highlights fall within the response of digital sensors, but that's really the same information just adapted to the sensor's response curve.
Originally Posted by MattKing
The book is really all about principles, and how light works, taking into account different kinds of objects, reflections, angles, revealing shapes, surfaces, contours, etc. There are whole sections on lighting transparent objects, metals and reflective surfaces, portraits, etc. It's not a cookbook, but if you learn what's in the book, you shouldn't need cookbook "place your lights here, here, and here" to get what you want instructions, your results will be more predictable, and you'll be able to work with whatever you have at hand.
Any edition should be good, as light still behaves the same way as before digital photography, and there's little to nothing about specific lighting equipment.
Here are some good used prices for all three editions: