iTunes 7 and higher allow one to use an iPod to transfer songs purchased through iTunes to as many as five authorized computers.

In the official company FAQ, Apple originally stated that:

Synchronization occurs only in one direction, from your computer to your iPod. This means you cannot transfer music, automatically or manually, from your iPod to a computer, and you cannot use iPod to copy a music library from one computer to another.

With the release of iTunes 7, Apple revised the company FAQ to note (emphasis added):

Synchronization generally occurs only in one direction, from your computer to your iPod. This means you typically cannot transfer music, automatically or manually, from your iPod to a computer, and you cannot use iPod to copy a music library from one computer to another.

An exception to this is the transfer purchases feature which allows you to restore purchased iTunes content to your computer from your iPod. Additionally, if you legally are allowed to copy music or other media files, you can configure your iPod as a storage drive to move media files.

iTunes 7 and higher allow one to use an iPod to transfer songs purchased through iTunes to as many as five authorized computers. This only works for songs purchased through iTunes, not those ripped from CDs or downloaded from other sources, which are much more common.

This restriction was designed to discourage casual music piracy, but unfortunately, this also prevents one from easily copying legally acquired music from one's own iPod to their own computer.

If you need to restore a music collection lost due to a system crash or want to transfer thousands of songs to a new computer using your iPod rather than again rip hundreds of CDs, fortunately, there are a number of easy to use freeware and shareware programs that make it simple.

For MacOS X, try Broken Helix and Senuti (and PhoneView for the iPod touch). For MacOS 9, try escapePod and iProber. For Windows, try SharePod and YamiPod (and TouchCopy for the iPod touch). For Linux, try GUIPod as well as YamiPod (which supports MacOS X, Windows, and Linux).

Visitor Contribution:

If you're using Windows, you also can just plug the iPod in, open the iPod in Windows Explorer, and enable the viewing of hidden files. For this example, we'll say the iPod mounted onto the I:/ drive. Navigate to I:/iPod_control/Music (again, note these are hidden folders and you will need to have viewing of hidden folders enabled for this to work).

In that folder will be subfolders named F00, F01, F02 and so on that contain all your songs -- the files will have odd names, usually 4 random letters -- however the file information for each file contains the actual information, so you can also just access the files directly this way.

This method additionally can be used to listen to your iPod while it is charging and displaying the "Do Not Disconnect" message by pulling the files into a media player application.