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[Corey Wilson <corey_wilson AT earthlink.net>]

Right.  The term "public domain" was being used incorrectly.  The 
requirement of prior art at issue can be met if the software is "known 
or used by others in this country, or was patented or described in a 
printed publication in this or a foreign country." 

To overgeneralize: a piece of software, open or closed, can be used as 
prior art as long as it (or its description) was available to the public 
one year before the filing date of the patent. 

My apologies for the careless use of verbiage.

> GPL'd software is most certainly *NOT* (capital N-O-T) in the public
> domain.  Works in the public domain do not have copyright, and do not
> have any restrictions on their use.  GPL software is copyrighted, and
> indeed, the whole legal force behind the GPL is because of copyright
> law.