I submitted this through the news feature option, but thought I should post it on the forum as well.
The Journal of Political Economy (Volume 115, Number 1, February 2007) has published a paper by Felix Oberholzer-Gee (Harvard University) and Koleman Strumpf (University of Kansas) with one of the most strongly worded statements I've seen on this issue:
"Downloads have an effect on sales that is statistically indistinguishable from zero. Our estimates are inconsistent with claims that file sharing is the primary reason for the decline in music sales during our study period."
This appears to be a re-write of this paper, released in March, 2004.