If you upload a very popular video, perhaps one that has millions of views, it racks up enough monthly views to represent a very steady traffic stream. That said, why not monetize the videos that you upload with an ad via the YouTube annotation tool?
Users are using the annotations as text ads for other products. Of course, what you can link to in the annotations is limited, but at a minimum you can link to other YouTube videos, and promote other products with plain text.
It is quite ugly, as you had imagined. Take a look at this example:
But while YouTube keeps its Partner program locked down, keeping most YouTube uploaders from profiting from their video, expect this form of advertising to just grow. YouTube just gets bigger and bigger, giving users even more incentive to try and extract monetary value from their videos.
How long until we see an underground ad network for this kind of advertising?