Here's one example use case where the ads are horrible: playlists.
Youtube has these "top tracks" playlists. When I discover a new artist, I'll often put that on and go do something else.
If a rollover ad comes on, I have to come back to the computer, and click the "skip" button, since I'm not sitting down.
One thing I was wondering: does the content creator make money when I skip the ad, or only when I take some kind of action based on it?