AFAIK, the cooling system in the iPod is not designed for constant spinning of the hard drive. This is why although you can boot OS X from an iPod, it's not recommended, as OS X is always using the boot drive as a swap partition by default, and may be constantly accessing the drive at times.
I know that the one time that I used my wife's iPod to copy raw video (not to edit, just copy), it got extremely hot...