Garr Reynolds has a good summary of the newest PowerPoint controversy started by this article in the Sydney Morning Herald that describes a study suggesting speakers who essentially read their bullet points from their slides are ineffective communicators.  The study's author suggested:

It is effective to speak to a diagram, because it presents information in a different form. But it is not effective to speak the same words that are written, because it is putting too much load on the mind and decreases your ability to understand what is being presented.