This is up there with the coolest uses of modern technology that I have ever seen. You need to watch this video to believe what Axa, a Belgium insurance company, did to promote their iPhone app.
interactive video
An Absolutely Brilliant YouTube Campaign by Tipp-Ex
With some bad language and some volume issues, this is up there with the most brilliant YouTube campaigns I have ever seen. It is a campaign for a brand of white-out called Tipp-Ex and brings Web internet video interactivity to a whole new level.