Having a pool of computers grabbing some info from one user and some
more bits from another source, then another source seems a little too
open for foul play.
Not a problem, each piece is hashed and checked. Anyone feeding you more
than a few bad chunks (accidents do happen) gets banned (and you accept
no more from them). Only possibility I can see for foul play is if the
original seed was a trojan. And that can be checked for with public
md5sums, which already exist. (Ie: Downloading things from suprnova.org
is potentially hazardous, especially to Windows systems.)