Apple issued an important update for Apple TV users today that fixes a bug that could cause content to disappear.

Users were informed via e-mail that if they downloaded the 3.0 update that they should subsequently update to the new 3.0.1 update. 

According to the e-mail and a support note, "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."

You can download this update by selecting Settings > General > Software Update from the Apple TV menu.