For some reason, I can't find D.O documentation on the proper folder permissions for Drupal on Linux. So for those of you a-searchin', here's my setup:
Edit: the handbook page is http://drupal.org/node/244924 (from comment), so go there to see alternatives and discussion.
cd /var/www
# u=rwx,g=rx for security
sudo chown -R {username}:www-data .
sudo chmod -R 750 .
# Let apache write to sites/{sitename}/files directories
find . -type d -wholename "*/sites/*/files" -exec sudo chmod -R 770 {} \;
# Make sure newly-created files retain the www-data group (useful for Drush)
# You don't want to apply this to files, only directories. Hence the round-about method
sudo chmod g+s .
find . -type d -exec sudo chmod g+s {} \;
