It has been occasionally noted that Greasemonkey is a hacker's tool. I take some pride in that, since I come from a family of relentless hackers.
My father was a landscape contractor who moonlighted doing home renovation. Sometimes, he worked on other people's homes, but he mostly focused on our own. My childhood living arrangement was in a constant state of refactoring. At one point, it featured a giant saltwater aquarium mounted in the living room wall and a freshwater koi pond with live turtles in the entry-way. My dad drilled an eight-foot-wide hole in our home's foundation, dug a hole in the dirt beneath, cemented it, and filled it with water, rocks, and fish, without any training whatsoever. He read a few books and figured out the rest on his own.
My mother and stepfather own a landscape-maintenance firm, but they are also tireless improvers of their surroundings. At this point, I think their home is at least 50% custom-built. They are architecting the next one themselves from scratch. Finding that none of the canned blueprints for mountain cottages adequately addressed their lounging-on-the-front-porch-on-Saturday-morning needs, they determined they had no choice but to draw their own.
This desire to improve one's surroundings isn't limited to my crazy family. And despite our love for big trucks and Home Depot, it isn't strictly an American thing, either. Hacking can be traced all the way back to the first Homo sapiens crafting stone cutting tools. To hack is to be human. Our species' entire history can be defined in terms of creating new tools to make our lives better.
Greasemonkey is a tool for making your life on the Web better. Think of it like a power drill for the Internet: fast, efficient, flexible, useful for a variety of tasks, easy, fun, and generally a good thing to have around the house.
You won't use it to build fine furniture, but when you just need some more shelves for the cupboard, it's the perfect thing.
But even with a great tool, you need a good teacher to show you how to use it and ensure you don't hurt yourself. Mark Pilgrim is a master writer and teacher. His Dive into Python is the bible for Python programmers and the book that I turn to most often when using that language. His previous Greasemonkey work, Dive into Greasemonkey (http://www.diveintogreasemonkey.org), is Greasemonkey's definitive online reference. Without his simple explanations and painstaking documentation, the Greasemonkey community couldn't have grown into the worldwide collection of programmers, IT professionals, and hobbyists that it is today.
If you read and understand the examples in this book, you'll become a member of this community. More important, you'll be well on your way to becoming a master of your web environment. The next time you find yourself frustrated by a broken web site, you won't have to live with it. You'll have the tools and knowledge to fix it yourself.
Creator and Lead Developer of Greasemonkey