Scot McKnight is ranting about PowerPoint and is trying to justify why he doesn't use it in his classroom. He's got a good list of reasons.
I'm a bit more open to PowerPoint presentations than Scot -- as long as we're not talking about a daily dose of them. The real problem with PowerPoint presentations is that they are presentations. It's not the technology per se but the underlying assumption that you can teach by simply presenting a series of slides. Yes, slides can be helpful at times. But they tend to transform students into audiences. And they can lock teachers onto a path in which there is little room for deviation. That is, it's hard to change directions when using PowerPoint and student discussion isn't as sequential as the slides. The temptation will be to minimize the moment so you can get through your presentation.