What is com.apple.Dont_Steal_Mac_OS_X

It is explained in the extension itself:

cat '/System/Library/Extensions/Dont Steal Mac OSX.kext/Contents/Resources/English.lproj/InfoPlist.strings'

Copyright 2006,2009 Apple Inc. All rights reserved. The purpose of this Apple software is to protect Apple copyrighted materials from unauthorized copying and use. You may not copy, modify, reverse engineer, publicly display, publicly perform, sublicense, transfer or redistribute this file, in whole or in part. If you have obtained a copy of this Apple software and do not have a valid license from Apple to use it, please immediately destroy or delete it from your computer._..Don't Steal Mac OS X

http://forums.macnn.com/90/mac-os-x/335611/dont-steal-mac-os-x-kernel/

Your karma check for today:
There once was was a user that whined
his existing OS was so blind,
he'd do better to pirate
an OS that ran great
but found his hardware declined.
Please don't steal Mac OS!
Really, that's way uncool.
(C) Apple Computer, Inc.

In addition to putting the "Your karma check for today: ..." string in memory,

I think it contains the code that decrypts certain other encrypted kexts and the Finder (which is partially encrypted, too).

Some of the hacks to make OS X run on non-Apple hardware distribute the encrypted kexts and the Finder in an unencrypted format, which makes it easy to go after them for DMCA violation (circumventing encryption for the purposes of infringing copyright). Distributing an unencrypted kext, which is copyrighted by Apple is distributing copyrighted works without a license.

(From the same link as Marc's answer)