Another reason automated slide shows suck is that they assume that the person creating the slide deck knows what they're doing, and has a reasonable amount of (i.e., not much) information on each slide, and that the density of each slide is roughly the same. In practice, most slide shows feature huge amounts of badly formatted text on at least some slides (not to mention the odd complex graph or diagram), which means that the amount of time needed to understand each slide can vary widely.

As Scott mentions, slide shows that include narration are a different story. For example, Larry Lessig's 2006 LinuxWorld conference keynote, Free Culture: What we need from you, is presented as a video. (Lessig also has a number of other videos of talks available using this style of presentation on his site.)