The Early Years...
I was one of those eager college grads that went and read the GOF's Design Patterns. Being pretty fresh to development in a professional setting, I used design patterns everywhere, even where they didn't belong. I've also read a ton of books on OOP and software architecture and they had a huge influence on my past projects.
Now that I've been at it for about 10 years, I've seen a sharp decline in the number of design patterns I use. In terms of UML and OOP, I barely even think about them anymore. Some of it's just that I'm so familiar with them that I don't really notice when I'm using them. The rest is because I just don't find myself reaching for them as often as before. Recently, I've noticed a sharp correlation between the use of abstract classes and increased code complexity. So, I usually rely on composition and helper classes for my shared functionality. I use interfaces mostly to support dependency injection and unit testing.
Every now and then, I whip out the Deco