Guy points to tips from the DEMOGod from DEMO 2006 which is kinda like American Idol except you get six whole minutes to talk to a gaggle of VC investies.
I like this one:
Practice Failing: No matter how much you prepare, something can still go wrong. Fortunately for us, our product worked great. However, the day before, during our technical rehearsal, the product froze.
Things can always go straight to hell when the screws are tightened. Never underestimate a backup of screenshots and JPEGS.