Reading this topic, I remembered of something that always bugs me.
There are certain practices, methodologies, or whatever, that existed for a long time, were well known and used. And then someone wrote a book, put a new fancy name on it, and out of nothing it starts to appear as something new, revolutionary, the next big thing, etc etc...
Design Patterns are a mix of well known solutions, that matured and become "collective wisdom", they´re not universal laws, and wasn´t created by GoF. You don´t need to read the book to apply some of them instinctively. The patterns evolved by themselves, GoF just glued it all together in a book.
As Phil Factor points out, Extreme Programming its nothing new too.
What other things makes you think "I´ve already seen this before..."?