Apparently NBC employ three people full time to trawl through YouTube and check for copyright infringement, but they seem to be fighting a loosing battle - as soon as something is deleted it's posted again by another user.
The endless legal issues faced by YouTube are surely going to force Google to moderate postings - an expensive and time consuming process - they're finding that, unlike with textual content, it's impossible to write code to parse, identify and screen the video content. Video is also a far more precious commodity than the written word; as much as a million dollars of budget has been poured into a minute's worth of content.
This does, however, remind me of the issues when remixes and sampling entered the music industry; initially there were lawsuits and then the industry came to terms with itself (in fact the artists were encouraged to resample from their own record label in most cases).
There have been elements of this with YouTube, as they do deals with the majors, but I suspect that the situation will become intolerable not just to Japanese broadcasters and Brazilian supermodels, but to many other organisations before long.
However, YouTube will not be alone in this predicament and it's all going to test the 'cases-and-desist' approach to policing hosting services to its very limit.