drush extension installation directory location Where is the recommended location to install drush extensions? 

I've downloaded drush_sup and have drush 5.4 installed. 

drush_sup/README.txt says to look in the drush README.txt file for the recommended location:


  See the Drush README.txt for locations where Drush extensions may be
  placed.


drush/README.txt does not discuss extensions.
This (the incorrect contents in the drush_sup README file) is a drush_sup bug report, and should go in the drush_sup issue queue.  I am the drush_sup maintainer, though, and can make this correction.

If you use Drush to download drush sup (i.e. drush dl drush_sup), then it will automatically be placed in the .drush folder in your home directory.  Drush automatically finds extensions stored in this location.