I've updated the REP based on the discussion here.  A diff of the
major changes is attached and you can view the full version at:

http://ros.org/reps/rep-0122.html

The major changes are:

 * Moved share/ spec to "Future Work".  The specification there is now
just documentation of the reference implementation, with notes on its
problems.
 * Adds Jack's recommended lib/ros/<package-name> as the likely way to
resolve the share/ specification, but notes it as work not-yet-done
 * A little more analysis on stack and package contents based on this layout.

 - Ken