Dave Winer has been ji'had-ing against the "amazingly bad" human interface of the iPod for a few days because, according to Dave, he plugged it into a new computer and it erased all of his iPod content without asking him. He's seen it multiple times now:

8:50PM Pacific: Plugged the video iPod into my desktop computer in Berkeley, and watched very carefully as it erased the contents of the iPod without confirmation. I didn't accidentally click OK giving it permission to erase all the content on the iPod, it did it without asking. Amazingly bad user interface.

Trouble is, I just don't buy it. I took an iPod and plugged it into a computer that hadn't seen that iPod before, and as expected, got this dialog box. Notice that "Do not ask me again" is not checked by default, nor is "Yes" the default button. If you simply press Return or Enter, nothing on the iPod gets changed. I accepted the warning and moved the iPod back and forth a few times to different computers, and every time, iTunes asked me if I wanted to "replace all existing songs and playlists on this iPod with those from this library." Every time, the default was not to do anything.

The only way I could get it to work the way Dave describes is to check the "Do not ask me again" checkbox, which I'm guessing he did at one point and forgot. iTunes provides several iPod warnings, including when it can't copy music in an incompatible format, or because it's purchased and your computer isn't authorized for it, and each of them has the "Do not warn me again" checkbox. I will agree that the interface for resetting these iPod warnings is hidden and needs improvement: Control/Right-Click on the iPod in iTunes's source list and pick "Reset Warnings".

In a sign of how correct the interface really is, iTunes tracks this stuff by computer, storing it in the iTunes preferences file, though not in a human-readable way (it's an XML-ified version of old-style Mac resources; remember that iTunes was originally a pre-Carbon application, so it's stored in what used to be a 'pref' resource). If you can't reset the iPod's warnings, delete the file "~/Library/Preferences/com.apple.iTunes.plist". You'll lose your iTunes settings, but you'll also reset the idea that it shouldn't warn you before erasing iPods.

If there is a way to convince iTunes to erase an iPod without warning that doesn't involve checking that box or copying a preference file from a machine where you did check that box, I don't know what it is.