Just to play the devils advocate for a while here, what is the actual consequence of this sharing? (Let's skip the moral pov completely).
Remember when C-cassette sharing was killing the music business? Piracy has existed long before the internet. What it does is make your products more widely known, and works as free grass roots level advertisement for your future products.
As an example, our EP has been out for under a month and I found a torrent sharing site that has shared it for over 100 times already. Of course it would be nice to have sold 100 copies in two weeks but let's be realistic here, how many people of those would've bought the ep or even known about it? I'm guessing zero. But our next album/gigs/t-shirts might sell a bit better because torrenting made it known to a wider audience. So I'm not advocating piracy, just saying there usually is a silver lining to it.
Yeah, that is also the other Point.. a lot of big bands are pushing the t-shirts these days more than the CDs or PM3s.