The latest version of iTunes (8.1) adds the Autofill feature to all iPhones and iPods, not just the iPod Shuffle where it's been available for sometime. The only problem with this new functionality is that it is really hard to find. If you want to turn on Autofill for your iPhone or non-Shuffle iPod, here's what to do.

1 - Connect your iPod or iPhone to your computer and open/go to iTunes.

2 - In the "Library" on the left side of the iTunes screen, click on your iPod/iPhone and then choose the "Summary" tab if you are not already there.

3 - Check the box next to "Manually manage music and videos" and then click on the "Apply" button.

4 - Now you can click on the arrow next to your device in the "Library" and then select "Music".

The Autofill options will then appear at the bottom of the screen. You can select the "Settings..." button to choose exactly how much space will be filled in by music as well as some preferences for how music is selected. You can also choose the libraries to use when filling your iPod or iPhone with music. When you have the settings how you want them, click the "Autofill" button then transfers the music to your device.