I want to add that if person wants a very OS X like desktop for GNU/Linux then Étoilé DE is very much the thing.

http://etoileos.com/etoile/

Only downside is that it isn't very mature yet. And in fact is in a need of developers. Alternative to Étoilé is the Window Maker with GNUStep and GWorkspace but it isn't everybody's cup of tea.

http://www.gnu.org/software/gnustep/