Well, I am both an OS X and a GNU/Linux user, so I have my 'feet' in both camps, if I may use that term.
OS X is what every computer user would want to use. It is easy, functional, stable, secure, it uses an advaced microkernel and IMHO is the most advanced (in technical terms) Operating System today.
BUT, there are a few things that OS X does not have. It is not a Free Operating System, in the sense that eventhough the underlying core may comply with the GPL and I mean the APSL under which Darwin is released, the overlying code is still proprietary and will probably remain so.
On the other hand we have GNU/Linux. A fully-featured, stable and secure Operating System, based on the notion of Freedom, with a capital F. Freedom to share, modify and join an ever-growing community of users, developers and activists.
On the technical side of things, Linux (and I am refering to the kernel here), is monolithic and that alone is a major drawback. Furthermore, the X Windows implementation that ships with virtually every GNU/Linux distribution is crappy (forgive the language
), and the recent dismemberment of the core team goes out to prove that those who were behind it were really slow into adopting changes and keeping up with them.
So, there is a + side to every OS, as there are -es as well. Please, do not ask me to comment on Windows