Check out this video of the new XGL/Compiz desktop for Linux. It is arguably a more graphically advanced desktop than even Mac OS X.
Take a look at what the next generation of Linux desktop looks like on this Linux video.
It uses Compiz and XGL to create a desktop interface that rivals or surpasses the slick look of Mac OS X. Notice the special effects when moving the windows around, and especially the desktop-switching feature, where you can switch between four virtual desktops by spinning them around like they are faces on a cube.
If you want to take Compiz/XGL for a trial run on your own computer you can try the Kororaa live CD.