I have a friend who co-wrote a book on TCP in the early days and it still sells because it hasn't really changed much in the interim. On the other hand, how ma

I have a friend who co-wrote a book on TCP in the early days and it still sells because it hasn't really changed much in the interim. On the other hand, how many times do you see something like Java 2.0 or C#2 books which are out-of-date very soon after the author has slaved over the whole process! The trick is obviously writing about something that won't change too much like Design Patterns and avoiding very specific things unless you are motivated by love!