Redirecting output from Drush
Drush (the command line interface to the Drupal CMS) is extremely useful, but inexplicably sends all output to stderr. If you're trying to redirect output of drush, you have to keep that in mind, using something like:
drush @site cache-clear all 2>&1 | tee -a $log
I always seem to forget since this behavior differs from the norm and I don't do this often enough to remember. Maybe now I will.