I agree with the first reply that the book is overrated. While it's not irrelevant, I wouldn't think it fits into a "must read" list for people learning software engineering. I often hear, "Head First Design Patterns" as a better reference if you're interested in design patterns. I own the GoF book, but have thumbed through Head First and am inclined to agree.

What I think is missing is the idea that design patters are often language smell. They're common patterns to compensate for deficiencies in the language. The GoF is most applicable to C++ code that uses a lot of OOP. Like the previous reply said, reaching for these patterns too quickly complicates things. Like using unnecessarily large words when simpler language would suffice.