Merlin, my presentation experience (in an academic environment that most would consider stuffy) has shown three things that inform my presentations, two as a presenter and one as an audience member. First, use a remote. If you have a Bluetooth cell phone, Salling Clicker is invaluable, especially with the Presentation Mode. As an amateur magician, I can palm my Sony Ericsson T637 so that it is pretty much undetectable to the audience. Second, since my presentations are usually academic research presentations, I outline my presentation in OmniOutliner Pro as I research and then export it to Keynote. Before this, I would get done researching a presentation and then have an "Oh, shit..." moment when I realized I had to actually prepare a presenation. Finally, use builds. I can't think of anything more irritating from a design and attention span perspective than when someone has a slide with five bullets on it and the whole thing is vomited up on the slide at once. If you do this, your audience isn't listening to you anymore; they are reading the rest of your slide. Your builds should be a cue to your audience that you're moving to the next point.

My wife, having taken lots of education courses in college, said that from what she could find, you have around 20 slides of attention span with your audience. After that, you lose them. In my academic context, I don't feel it's inappropriate to go longer than that, but your situation may be different.

Anyway, I hope those help.