from the info page..

Rescue the most important part of the disc first.

   ddrescue -i0 -s50M /dev/hdc hdimage logfile
   ddrescue -i0 -s1M -r3 /dev/hdc hdimage logfile

Then rescue some key disc areas.

   ddrescue -i30G -s10G /dev/hdc hdimage logfile
   ddrescue -i230G -s5G /dev/hdc hdimage logfile

Now rescue the rest (does not recopy what is already done).

   ddrescue -r3 /dev/hdc hdimage logfile

Example 1: Rescue an ext2 partition in /dev/hda2 to /dev/hdb2

   ddrescue -r3 /dev/hda2 /dev/hdb2 logfile
   e2fsck -v -f /dev/hdb2
   mount -t ext2 -o ro /dev/hdb2 /mnt

Example 2: Rescue a CD-ROM in /dev/cdrom

   ddrescue -b 2048 /dev/cdrom cdimage logfile
   write cdimage to a blank CD-ROM