Did a little digging around. It looks like they manage to get discovery judgments all the time over partial downloads, but I don't see them actually taking anyone to court for anything less than a full file.

Once you have the entire file available, it's hard to shimmy around the distribution claims. Wouldn't it be super effing interesting if everyone's torrent client specifically picked a random block and refused to give it to anyone?

I'm not sure it would hold up in court, but it would be interesting.