We have a pdf of slides with mockups and detailed specs for our product. Each page - a slide. Each facet of functionality - a set of slides. Each step and interaction a user can go through - a slide. As a visual reference for implementation, it makes life a lot easier than reading pages of textual specs, so it can definitely be useful.

On the other hand, this is not exactly the common powerpoint presentation, it's just a a deck of specs passed around in that format, so not the same thing at all in the end.