The iPad does not natively project its screen to an external vga device such as a projector. That can cause problems for teachers/instructors. There are some makeshift solutions - here's a short list of some of the ones currently available:
I can't say that I'm crazy about any of them but these sorts of apps address a real need on the iPad and more are coming out every few days.
I've just joined and am excited to be part of this community. As part of training and conference talks I need to project the iPad itself, rather than supported apps. This (alongside the ability to be able to make screen recording videos of the iPad) were two of my principle reasons for jailbreaking the iPad. With DisplayOut and DisplayRecorder from the Cydia store those two are very possible.
I've written a few blog posts on my experiences with the iPad here:
A man after my own heart ... :) Yes, jailbreaking apparently will allow users to project. I have also heard that there are apps that will allow you to display flash if the iPad is jailbroken (I assume that's the correct past tense...?).
Having said that I did jailbreak my iPhone a few months ago and have to admit that it ran so amazingly slowly that I reverted back to the regular Apple OS.
I think the jailbreak on the iPhone and the iPad give very different results. My iPhone (3G) is slow these days due to the Apple update... jailbreaking didn't slow it down any further. On the iPad I've noticed no change in speed, and no change in battery life at all. The advantages (multitasking, useful apps...) make it worth the three minutes it takes, I reckon.
My favorite classroom app for projecting PowerPoint or Keynote slides, pdf, Excel, and video is 2Screens - Presentation Expert. There is also a 2Screens Remote app for the iPhone/iPod Touch for remotely controlling 2Screens on the iPad via Bluetooth. I have been using these 2 apps together in a university classroom and they work very well.