Customizing OS X isn’t the easiest thing to do if you’re the type of person who likes to tinker and make things your own. There isn’t exactly a nice button you can push to turn off all those skeuomorphic features around iCal and Address Book. But, what you do have access to is a bunch of terminal hacks to toggle some features on and off.
For instance, from the terminal you can enable a 2D dock, make icons of hidden applications translucent, and even completely disable auto-correct in Lion. Mathias Bynens has put together a giant list of default hacks on Github that gives you the commands you need to hack away at OS X.
What are Defaults? According to Apple:
Defaults allows users to read, write, and delete Mac OS X user defaults from a command-line shell. MacOS X applications and other programs use the defaults system to record user preferences and other information that must be maintained when the applications aren’t running (such as default font for new documents, or the position of an Info panel). Much of this information is accessible through an application’s Preferences panel, but some of it isn’t, such as the position of the Info panel. You can access this information with defaults
If you’re into hacking your operating system, you should certainly check out the list. It’s worth a look.