Backup an SD card on Linux using 'dd'

#!/bin/bash
if [ -b "/dev/$1" ]
then
  outfile="sdcard-backup-`date +"%s"`.dd"
  echo "cloning /dev/$1 to $outfile"
  dd if=/dev/$1 of=$outfile
  echo "tgz-ing $outfile"
  tar zcvf $outfile.tgz $outfile
  echo "done."
else
  echo "Usage: $0 /dev/<device>"
fi
echo "to restore, unmount(?), then use:"
echo "tar Ozxf <file> | dd of=<device>"