My trusty MacBook Pro always had problems with the Dock's animations (opening an app that isn't in the Dock, icon bounces, minimising etc.) that would slowly get worse and worse over time. The frame rates of these animations would slow down, resulting in the most horrifically jerky Genie effect ever. The only way to fix it was to restart the Dock. Although it doesn't sound that awful, it really ruined Leopard's slick user experience for me. I remember reading previously that the problem may have been caused by a video memory leak... something to do with the NVidia drivers, perhaps. It seems that in Snow Leopard all of the Dock animations, including the lovely new Stacks, are super smooth, back to how they were in Tiger. I remember hearing similar stories from users of other Intel Macs, but it appears that this little (but very annoying) problem has been solved.