Just because the OS X installer doesn't require you to input a 20 digit product key doesn't mean that you're free to ignore the license agreement that you agreed to before installing the software. On any ordinary copy of OS X (and I'm sure Leopard is no exception), the EULA specifically states that you are allowed to install the software on one licensed Apple machine (with the exception of the OS X family pack, which grants up to 5 computers in a home). If you break the license agreement, you break the law. It's that simple.

Simply, as you can only install OS X on a computer you bought from Apple they are less concerned about piracy than Microsoft .

If everyone pirates Windows, Microsoft goes broke, but if everyone pirates OS X, Apple at least got (a lot) of your money when you bought the computer you installed it on and therefore can afford to trust its customers more than Microsoft can.

Really they don't have a problem, since the only people who pirate OSX are almost always just doing an upgrade

Mac OS X Server , keynote and some others DO need a key though

Thanks for that guys. I thought that might be the case but i wasn't sure. Don't worry i don't actually plan on installing it on more then one computer especially considering the fact that we have bought a copy for each Mac that we have within the charity. I was mainly just curious about the fact that i had not seen anything like a CD key or something to distinguise the disc.

It makes more sense that apple do it that way. Less time spent on stopping people from illegally distributing and installing the OS and more time to develop the cool features that we all know and love about Mac