... spring really seems to be here. Copenhagen is bathed in sun today (when the clouds aren't shadowing, mind you).
As we all know MacOS X is build upon a Mach microkernel and FreeBSD. The BSD-style license is okay with that, people are free to use the code to create whatever they want - and not release it back to the people who built the original. The GNU GPL is different in that it demands that derived programs must be released under the same license. Some would say that MacOS X is an example of a company taking advantage of all the good that the FreeBSD-people have done without giving much back.
Some people think the GNU GPL is too restrictive (with it's "viral" design, forcing people to continue to share), some think that the BSD-style license is too weak - letting people/companies get away with too much. Hard call. I tend to prefer the GNU GPL, because I like the sharing aspect: I allow other people to play with my toys, but when they make it better, they have to share the improved toys with me, as I shared my toys with them in the first place. Sharing, helping each other, cooperating, standing on the shoulder of giants: Free Software.