
This article claims that YouTube is going to start removing uploaded user-made content that uses copy-protected content. This is going to be a massive undertaking and could have major repercussions for YouTube. Whether or not 'copyright protected music' will apply only to mainstream audio or whether this will kill the fake trailer market is unknown. But so far, the crackdown has been pretty pervasive and thorough. So far the trailer market is seemingly safe while the fanmade music video industry has been nearly wiped out overnight.

Amazingly, I never had this problem when Ally wants to dance to 'The Safety Dance' or 'Crocodile Rock'.
Scott Mendelson
My favorite trailer mash ups of late (animated mash-ups are the best, as you can actually get the lips to match):
'The Incredible Quantum of Solace':
Not only is the matching work impeccable, this also gives us the kind of pure action trailer that the actual Incredibles campaign denied us.
The Dark Knight trailer 01 (done in Batman: TAS style)
Of the many, many Dark Knight trailers done up in one version of Batman (the Tim Burton film, the 1960s show, etc), this is by far the most polished.