In iTunes, you have the option to download album cover art directly, so it will show up on your iPod as you casually flip through CDs like they do in those iPod commercials. I recently wiped my iPhone and its music (intentionally), and since I am starting over, I am determined to get all the cover art for every CD I add. Sometimes iTunes, for whatever reason, is unable to find the artwork and you have add it manually.
Other times, iTunes will automatically add the wrong album cover. For example, iTunes believes this is the appropriate cover art for the RENT soundtrack:
It appears to be the soundtrack to some kids’ movie. I’d be lying if I said I wasn’t a little curious to see it.