PowerPoint should be thought of as much more than presentation software. Through the use of action buttons and other aspects of PowerPoint students or teachers can create interactive stories such as the download below. Here is a link to some notes on how to use action buttons with PowerPoint 2007.
One of the problems with using PowerPoint is that you can't easily embed an interative slideshow such as this example directly into web 2.0 spaces. Using third party sites such as Slideshare you can however embed unidirectional shows such as below.
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