http://http.us.debian.org/debian/dists/woody/main/disks-powerpc/current/doc/ch-hardware-req.en.html

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

Says:
=========
Some hardware manufacturers simply won't tell us how
to write drivers for their hardware. Others won't allow us access to the
documentation without a non-disclosure agreement that would prevent us
from releasing the Linux source code. One example is the IBM
laptop DSP sound system used in recent ThinkPad systems ? some
of these systems also couple the sound system to the modem.


IBM released mwave GPL drivers and info a long time back now, and its in
the base kernel. Pick a newer evil example - say Nvidia ?