Howtoforge posted an article about how you can change the appearance of your Ubuntu 11.04 desktop (with the Ubuntu Classic interface, i.e., GNOME instead of Unity) so that it resembles a Mac.

This can be achieved with the help of Elementary, Docky, and Gloobus-Preview. Elementary is a project that provides a popular icon set and GTK theme; Docky is an interactive dock (like the one you know from a Mac) that provides easy access to some of the files, folders, and applications on your computer, and more; and Gloobus-Preview is an extension for the Gnome Desktop Environment designed to enable a full screen preview of any kind of file or directory.

  How To Make An Ubuntu 11.04 Classic Desktop Resemble A Mac