Another advantage of using SuperDuper (Leopard compatible now?) or Carbon Copy is that the new drive is created with all the files deframented!
When I upgraded to Leopard, I used CC to clone my Laptop (5,400 rpm drive) to an external 7,200 rpm drive (FW800 connected) to back up my Tiger installation which was taking so much time to boot. Using the cloned drive to boot via FW800 cut down the boot time by a third!