Some years ago an article mentioned Scott McNealy noticed amount of data being sent back and forth, and also amount of time people spending on preparing PPT. So he banned Powerpoint and there was noticeable increase in productivity, people actually doing stuff instead of futzing with PPT slides (though I also heard there was zero MS products on desktop computers at Sun so not sure how PPT was originally in place). For me when I do PPT, I typically do it in MS Word with pages in landscape orientation, then save it as PDF. When I gotta do PPT, I try to keep minimal cutesy graphics.
But maybe the whole concept of PPT type slides including old school viewgraphs and charts leads to people making bullet lists that contain contradictions. Like what Feynman pointed out of a slide NASA used for describing Shuttle ops and priorities and he marked two sentences that contradict each other, which was a contributing factor of leading to dangerous situations. I can't remember the details but it was one of those "yeow, we actually made that mistake?!?" moments.