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A good example is a product that I purchased a while back for a video project. It's a camera mount that uses big suction cups to attach to a moving vehicle.
The company has gone crazy with demonstration videos - showing not only the usual application attaching it to a car in various positions, but to boats, airplanes, etc.
Using YouTube offloads their server load for these videos, but at the same time the videos are cool enough to appeal to a broader audience. I'd bet they get quite a few customers from people stumbling across their videos on YouTube and saying "hey, I want to do that!"