If you're clicking on an ad on YouTube, then somebody is making money--usually the artist and YouTube.
When we're talking about monetization, there's no magic to it. I mean, this is a familiar business model to the content industry. It seems new, and we say “new media”, but ad-supported content is as old as the hills, right?
What's new about it is that it's measurable and it can be targeted. It can put relevant ads in front of you. For example, if I am reading a magazine--and magazines are largely an ad-supported medium--and there's an ad for Lexus cars, well, that ad is irrelevant to me because I have a Honda and I'm not in the market for a car.