When I have to work with OS X, my favorite editor is Aquamacs, an OS X version of Emacs. One thing that always annoyed me with Aquamacs is, that the kill-ring, Emacs' internal clipboard system, is not synchronized with the OS X clipboard. Don't ask me why, the authors of Aquamacs seem to think it is a good idea since it is an item on the feature list.
However, today it annoyed me so much that I searched the interwebs for a solution and I find a rather easy one:
(setq x-select-enable-clipboard t)
That's it. Nice :-)