[IsTom]

You can download and share only selected parts of a torrent. With enough people you're going to get full coverage anyway.

[nicce]

Assuming that people randomly select the portions.

[vincnetas]

how do you coordinate who downloads which part?

[IsTom]

Torrents track availability of pieces, you can seed ones with least availability if you want that.

[WhyNotHugo]

Potential attack vector: seed excessive copied of a portion from many sock-puppets. Wait for non-sock-puppet seeds to dwindle. All the existing copies are now under your control.