Prior to attempting to run my 'Pi at 1000Mhz I decided it would be a good idea to backup the entire machine.As it uses a 4GB SD it made sense to use another 4GB card as the backup destination. As it turns out it was simpler than I expected.
I placed a new 4GB SD card in a USB card reader and inserted into on of the 'Pi's USB ports. I then checked to see what device node the 'Pi used for the card. In my case I found the card at '/dev/sda', and that it has not been automatically mounted. In my case it was not automatically mount but other/future version of 'wheezy' may do this so it is important to use the 'mount' command to check this.
The following command line shows how I block copied the entire content on the operating system block device '/dev/mmcblk0' to the unmount SD card at '/dev/sda'.
sudo dd if=/dev/mmcblk0 of=/dev/sda bs=4M
root@raspberrypi:/boot# dd if=/dev/mmcblk0 of=/dev/sda bs=4M
945+1 records in
945+1 records out
3965190144 bytes (4.0 GB) copied, 840.205 s, 4.7 MB/s
To test I simply placed the new card into the Raspberry Pi and up it came, a perfect clone!
As it turns out, my 'Pi failed to start at 1000Mhz
so the effort was well worth it 
.... Robert
