An example on how to use duplicity to perform encrypted incremental backups on Google Drive. Changes over tileo's original script: Google Drive instead of S3 as backend storage. Zenity dialogs to ask for credentials. IGNORE variable to exclude a list of directories from the backup. Verbosity raised to level 8. Activated asynchronous uploads.

duptools-gdrive.sh

#!/bin/bash

# directories to be included, space separated
SOURCE="/home/chewie /etc"
# directories to be excluded, space separated
IGNORE="/home/chewie/Downloads /home/chewie/Steam"
DRIVE_FOLDER="duplicity-backup"
LOGFILE=/home/chewie/duplicity.log
# set email to receive a backup report
EMAIL=""

get_credentials() {

  gpg_pass="$(zenity --password --title 'duplicity - GnuPG passphrase')"
  google_credentials="$(zenity --password --username --title 'duplicity - Google Drive password')"

  case $? in
    0)
      google_username=$(echo $google_credentials | cut -d'|' -f1)
      google_password=$(echo $google_credentials | cut -d'|' -f2)
      ;;
    1)
      echo "Stop login.";;
    -1)
      echo "An unexpected error has occurred.";;
  esac

  DRIVE_URL=gdocs://$google_username@gmail.com/$DRIVE_FOLDER

  export PASSPHRASE="$gpg_pass"
  export FTP_PASSWORD="$google_password"
}

backup() {
  INCLUDE=""
  for CDIR in $SOURCE
  do
    TMP=" --include  ${CDIR}"
    INCLUDE=${INCLUDE}${TMP}
  done
  EXCLUDE=""
  for CDIR in $IGNORE
  do
    TMP=" --exclude  ${CDIR}"
    EXCLUDE=${EXCLUDE}${TMP}
  done
  # perform an incremental backup to root, exclude directories, include directories, exclude everything else, / as reference.
  duplicity -v8 --asynchronous-upload --full-if-older-than 30D $EXCLUDE $INCLUDE --exclude '**' / $DRIVE_URL | tee $LOGFILE
  if [ -n "$EMAIL" ]; then
    mail -s "backup report" $EMAIL < $LOGFILE
  fi
}

list() {
  duplicity list-current-files $DRIVE_URL
}

restore() {
  if [ $# = 2 ]; then
    duplicity restore --file-to-restore $1 $DRIVE_URL $2
  else
    duplicity restore --file-to-restore $1 --time $2 $DRIVE_URL $3
  fi
}

status() {
  duplicity collection-status $DRIVE_URL
}

if [ "$1" = "backup" ]; then
  get_credentials
  backup
elif [ "$1" = "list" ]; then
  get_credentials
  list
elif [ "$1" = "restore" ]; then
  get_credentials
  if [ $# = 3 ]; then
    restore $2 $3
  else
    restore $2 $3 $4
  fi
elif [ "$1" = "status" ]; then
  get_credentials
  status
else
  echo "
  duptools - manage duplicity backup
  
  USAGE:
  
  ./duptools.sh backup 
  ./duptools.sh list
  ./duptools.sh status
  ./duptools.sh restore file [time] dest
  "
fi

unset PASSPHRASE
unset FTP_PASSWORD

What version of duplicity are you using? Does it work after ClientLogin deprecation?