Originally Posted by doogald

This is not 100% true.

First, when you delete a song, it asks if you want to remove it from the library or put the file in the trash. Take the first option and it's not that hard to get the song back; the second isn't too hard, so long as you haven't emptied the recycle bin.

Second, if you are talking about a song purchased in the iTunes Store and you have synced with an iPod/iPhone, the next time that you attach the device to sync after deleting a song from iTunes it will inform you that there is purchased content on the device that is not in iTunes and will ask if you want it synced back to iTunes.