This is actually perhaps something rather significant... For once, a judge has ordered that the burden of proof for fair use is laid upon the plaintiff instead... Personally, I think that this is a good idea, since this should cut down on that huge slew of frivolous lawsuits filed by corporate copyright holders against small individuals in such a way that they are dissuaded from attempting to take up that burden and hence defend themselves.
As far as actual "fair use" goes, the bulk of YouTube videos almost invariably well pass on criteria #1, #2, and #4, as they, in respective order, are done for a non-profit/non-commercial/personal-only usage, take from a copyrighted work that is already openly available, and as a general rule, do not degrade the value of the copyrighted work; i.e, it does not hamper the holder's ability to make money off of the work.
That only leaves #3, the question of the amount and substantiality of the work. It should be noted in cases where the copyrighted content that is used is entirely parodied, then it passes this criteria as well.
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