Mac users have always appreciated "Easter eggs", or little tricks and hacks hidden deep in the system, system tools, and applications. The very first 128K Mac featured a hardware version: The signatures of the Mac development time molded into the plastic case.
The Easter Egg Archive has a nice list of Mac OS X Easter eggs. Some can be reached only through the Terminal. The Easter eggs are listed in order of scores they've received. All are interesting.
The top Easter egg, with a 9.2 score, isn't really much of an Easter egg. But it is cute. It's about the text to Here's to the Crazy Ones from the Think Different ad campaign introduced at the October Seybold Seminars San Francisco in 1997.
In the icon for TextEdit, you can see some text. What is it? It's a very important piece of Mac and Apple history.
Here's to the crazy ones. The misfits. The rebels. The troublemakers. The round pegs in the square holes — the ones who see things differently. They're not fond of rules and they have no respect for the status quo. You can praise them, disagree with them, quote them, disbelieve them, glorify, or vilify them. About the only thing that you can't do is ignore them. Because they change things.
According to the archive, the double cuteness is that John Appleseed is the sample name used to demonstrate Mac applications such as Address Book or on the iPhone; and Kate is an open-source Linux text editor in KDE.