Tufte's booklet on slideware arrived and it lives up to my expectations.

Basically, the message is that typical PowerPoint slides convey extremely little information, but (quoting Tufte) the damage is mitigated since meetings relying on the PP cognitive style may not matter all that much. At least these meetings have a consistent concept then: say nothing, and use inefficient tools to say it...

He also uses the enlightening Gettysburg PowerPoint presentation as an example. I'm burning my PowerPoint CDROM as we speak ;-)