Apple is warning that you should update your Apple TV asap to avoid losing your media:

There is an issue with Apple TV software version 3.0 that can possibly cause your content to disappear after a period of time. All customers running Apple TV software version 3.0 should immediately restart their Apple TV and then upgrade to Apple TV software version 3.0.1.

For either symptom, do the following:

1. Restart your Apple TV by unplugging the power cord and plugging it back in.
2. Select Settings > General from the main menu.
3. Select Update Software.
4. Select Download and Install when prompted.

Note: Your Apple TV will restart; this is followed by the Apple logo and a status bar.

According to Apple, the symptom of this problem is “You are using Apple TV software version 3.0 and all of your movies, TV shows, and songs appear to be missing,”

via Tuaw