They aren't nearly as useful as they are interesting in their design. They mostly focus on minimal pair discrimination, plus two preposition activities. This site contains a few lessons on American English and culture. Activities include weather, conversation, elections. Some activies for Japanese speakers with Japanese browser capabilities are also included.
Sound files are in .au and .aiff formats.
Audio files are in .au format. Illustrations and text are included, but there are no comprehension activities. Audio files are in RealAudio format. Activities include QuickTime videos demonstrating correct pronunctiation, tongue twister activities, minimal pairs, and dictation. If you have a Mac and a microphone, you can even download their net phone software and speak to native English speakers live.