I farm and have used some BT corn.  Chemical/Seed companies are urging users
of BT corn to always plant at least a 20% on farm refuge, into non-BT corn
for just such a situation.  They are aware of the possible consequences.  But
like most things that are good products, used irresponsibly they are a
disaster.  We seem to have a propensity for screwing things up.

:)
Mike