The new taskbar is a thinner and has a far more transparent background. The application buttons are thinner and wider, with a faint white border. The ‘hover’ state sports a trendy blue gradient button that reminds me of the new Vista Media Center style, also the Live Preview no longer reports the name of the application on top.
Overall, a subtle change over the current design, but makes the taskbar more aesthetically pleasing and cleaner. Also on a side note, there are two new icons on in the Quick Launch bar, although I do not know what they represent, presumably one is Flip 3D (right).