"The iPod, soon to be seen on CSI?"
Turns out Apple did some clever things within the iPod that should indirectly help criminal investigators and discourage would-be criminals. . . .
On a typical Windows drive, deleted files aren't really deleted, they are taken out of the master boot record, but the files themselves remain on the hard drive. The deleted files aren't accessible by users, but the space used can be and often is overwritten by new files. This can cause uneven wear on the drives. iPods are similar, in that deleted files aren't strictly erased, just marked as such. But Apple made it so that the tiny iPods write to the drive until the disk's real estate is used before rewriting space that holds files that are marked as deleted. For a criminal investigator, that's a boon: old data is less likely to be overwritten. If you did commit a crime, just deleting the evidence isn't going to help.
Better yet, iPods also remember where data came from. Say you used a computer at work to copy a large, top-secret program to your iPod to take home. Coding within the file would tell investigators not only what machine (MAC address) but also what operating system (though file format also tells them that) and username was used. So if incriminating evidence is found on your iPod, they can connect it to a crime scene. . . .
Of course, the downside of this for the law-abiding is that if you lose your iPod someone else is also able to get all the personal information that you have on it.