I quiet like some of the Leopard features, the 'OS X Previewing Framework' is quiet nice, if not ripped off from Vista's.. but I think they polished the UI experience a bit more..
One is flicking through various items, and finding a video, the video starts to play, and the user clicks on it, instantly it zooms up to take full screen control.
Sure.. Vista does this, but if theres something Vista still lacks, its the general animation and blending OS X has with its 'explorer'.