I imagine that this variable would likely be customized on a
file-by-file basis using "file local variables".

>>
>> Perhaps I could help by specifying what I'm trying to do? I'd like to write
>> an article or book about particular statistical analyses. I want this also
>> to be a piece of reproducible research so readers of the book can follow
>> along and perhaps analyze data of their own. I'd like to write a code block
>> once and then use it in the following ways: 1) evaluate and return the
>> results of analyses; 2) export as a floating listing so I can refer to it in
>> discussions of implementation; and 3) tangle to a source code file that can
>> be used as the basis for a package that can be used outside of Org mode.
>>

Sounds like a very cool project.  If this will be public I would love to
link to it from [1] when it is complete.

>>
>> 1) is easy with #+call: With the :wrap header argument that we've
>> partially implemented, I can mark the results off in whatever environment I
>> like, which is a wonderful bit of flexibility. Different kinds of results
>> can be presented distinctively.
>>
>> 2) is partially there--the code itself is handled nicely by minted and
>> I'm able to make it look as good as I want. What I'm lacking now is an easy
>> way to identify the code block. Seb's suggestion that the header lines be
>> included is one way, though Eric F.'s point about the special characters
>> tripping up LaTeX is well taken. It might be some work to get an
>> intermediate representation that can be exported to all the targets. My
>> alternate idea, which is to wrap the code block in an environment to which I
>> can attach a caption and a label, is the LaTeX approach and might not work
>> as well for other export targets.

This new solution replaces the code block with Org-mode text before
export.  This should be the most flexible as arbitrary #+HTML and
#+LATEX lines can be used in Org-mode.

Best,

Footnotes: 
[1]  http://orgmode.org/worg/org-contrib/babel/uses.html

-- 
Eric Schulte
http://cs.unm.edu/~eschulte/