Another suggestion - make sure that the person giving the demo knows the product inside and out. There's nothing that sabotages a demo like a question about the demo that can't be answered because the demonstrator doesn't know the intricacies of the product. This typically happens when the president/CEO is doing the demo, but wasn't on the team that built the product. At the very least, make sure that a product expert is in the room during the demo to answer any questions that might come up.