> (1) Is it legal for a commercial company to mix Free code
> with developed code? If so, what is the status of
> the combined code? How does that protect the Free code from
> becoming, say, non-Free?

PA = proprietary package A
GB = standard GPL package B
GD = package D under the "GNAT special exception"

Distributing program containing PA, GB, GD imposes standard GPL on PA
source.  Distributing program containing PA & GD has no effect on source
of PA, but requires distributor to comply with availability provisions of
GPL regarding GD.  The following seems sufficient to me (not a lawyer):

   Portions of this program are "free software" as defined in the headers
   of the source code.  This source was obtained from
   http://wwww.some.place.TLD.

Now if GD was modified for this program, the GNAT special exception does
not completely exempt the modified GD from the GPL.  So that could be an
inconvenience.  The special exception allows the company to preserve their
rights to their own code, but distributing their program still requires
them to "allow" people to get the modified GD source.

Would the situation be any different if GD was under Dave Weller's ACL?

How about the perl "artistic license"?

The GPL was designed not only to keep software free, but to encourage free
software.  That's where some people have trouble with it--they don't want
to be forced to "liberate" their own code.  (In some cases, they wouldn't
have to, but they overestimate the scope of the GPL.)  Here's a blurb that
ensures the covered software remains free, but which does not meddle at
all with anything else:

/*
 * Copyright (C) 1994 by Dave Glowacki
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * to rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT ..... etc.
 */