The study comes from the Japanese Research Institute of Economy, Trade and Industry, a prestigious think-tank for the Japanese government. They investigated the effects of YouTube and the Japanese P2P program Winny on the rental and sales of anime DVDs, and came to some interesting conclusions.
YouTube does not negatively affect DVD rentals, and it actually increases DVD sales. Winny, on the other hand, does negatively affect DVD rentals, but has no effect on DVD sales.
"YouTube's effect of boosting DVD sales can be seen after the TV's broadcasting of the series has concluded, which suggests that not just a few people learned about the program via a Youtube viewing," the study's abstract reads, "In other words YouTube can be interpreted as a promotion tool for DVD sales."
We're still in the middle of determining the effects of piracy on the market. You can talk about the financial aspect of the story all you want, but in the end, I find the effect it has on art much more important. Whether or not people make more or less money is of no relevance to me - what matters is whether or not piracy promotes the arts and sciences.
What we know for sure is that current copyright law has a detrimental effect on the arts and sciences. What we need to investigate now is whether or not piracy combats these detrimental effects of copyright law.
In the end, promoting the arts and sciences - the original goal of copyright - basically comes down to spreading them. I'd hazard a guess piracy has done more to spread especially the arts than copyright law has ever done.