Actually, when it comes to Mac OS X the replacing of libraries that Psystar or any other hackintosh-er had to do is in fact illegal. Major components of the OS (i.e. the Finder application binary) are encrypted and signed. For the system to be usable those binaries need to be decrypted during load with the help of the kernel extension "Don't Steal Mac OS X.kext." That extension does the tests to ensure that the system is running on Apple hardware and will only decrypt the binaries if it checks out. To get around that, the hackintosh community have come up with "decrypter" extensions that decrypt the system binaries themselves. As it happens, using one of those is a DMCA violation (reverse-engineering and bypassing DRM, effectively). On a related note, when Psystar started selling their machines much of the hackintosh community was pretty annoyed, as they were selling community-made tools (boot-132 loader and efi v8 emulator, if I remember correctly - boot-132 is APSL but PsyStar didn't release the source and pc_efi v8 is forbidden for use commercially).