In the past I have already tackled The argument by publishing guides on how to make a desktop based on KDE but VERY VERY similar to Mac OS X.
Sure they required to perform different tasks and take care of the various aspects individually.
Today I propose instead a complete package: Phoenix: Mac4Lin ver.1.0 Released! .
Unfortunately it is only available for the GNOME desktop, like Ubuntu, for example, while not function on the KDE desktop, as Kubuntu.
The appearance more interesting is that this package not only takes care of changing the desktop and windows to return apple style, but also various external programs such as Firefox, Thunderbird and Rhythmbox.
The result is quite good: