@aki,

Heh, it boils down to differing opinions of the word "freedom." ;)

GPL's definition of freedom is a "viral" one, meaning that derivatives of GPL software must also be be GPL.  To the BSD people this is restrictive.  BSD's definition is a less-restrictive freedom, in that you can do "whatever the fuck" you want to do with it, including print it on a roll of toilet paper and wipe your ___ with it.  You can also choose to give back if you want.  There is no obligation. :)

Also, while they're similar UNIX-like OSes, FreeBSD and Mac OS X don't share much more than the kernel.  Apple's userland is heavily modified, and the windowing environment is as proprietary as they come.  Darwin's only useful if you're into computer science research basically!

Alan