So, that's everyone, then? Based on my experience at computer science conferences, it's about 90% PowerPoint, 9.9999% PDF, and I saw one Prezi presentation once (and god, all the zooming about hugely distracted from the content).
And as kettch says, conference Wi-Fi tends to be very, very flaky. I want to have my presentation on my laptop's hard drive. And on a thumb drive, in case my laptop fails. And on SkyDrive (so I can download it, well in advance of the actual talk), in case the thumb drive also fails.
Yeah, I'm paranoid. But I've also never lost any data.