The scroll wheel on the 10 GB and 20 GB iPods is touch-sensitive, meaning that you "spin" just by gliding your finger in circles as you would if you were actually spinning it (a "click" sound follows each virtual movement of the wheel).
The 5 GB iPod is basically the same model as the one from before: it's the same thickness, probably the same weight, and has the conventional scroll wheel.
Actually I think it's a great move. When I use my iPod during class [yes, in class ] I sometimes make a jerky movement with my hand to get the wire out of the way. But my iPod is in that same hand. When I jerk it like that the scroll wheel moves and the volume goes all the way up. I keep getting the living bleeding blue heck scared out of me every time it happens.
But with the new iPod you can shake the iPod [I wouldn't recommend it ] and the scroll wheel wouldn't move, nor would the sensors for your fingers. This way, I can keep myself from going deaf.
Besides, what if you accidently put something on the wheel part of the [old] iPod and it turns? The volume goes up, again. The finger-sensative new iPod doesn't do this. It's basically a trackpad.