I do share the concern - I've fought a couple big battles on the issue of big site "content borrowing" just this year. Ultimately, it is a very big issue - and the question is for the courts to a large degree due to the complexity of the US "Fair Use" provisions.
And truthfully, I'd rather see it stay mostly in the courts. Although I have found Google to be an ally in the battle with YouTube infringement this year. They were ripping DVDs and VHS that my client had published and copyrighted in hard copy, so the case was dead-cold made.