Unlike a meeting where the presenters might be annoyed, the opposite is true; they'd like the audience to help them generate hype. This could be especially true

Unlike a meeting where the presenters might be annoyed, the opposite is true; they'd like the audience to help them generate hype. This could be especially true at a conference like Demo or Techcrunch50 where many products are being launched. You want people to be able to try it out right then and there. There are potential investors watching. More important could be the tech evangelists with huge followings watching. A blog post or even a tweet from them could be worth thousands of users. You want them to tweet you, get retweeted and generate that viral buzz.