Samsung S3 - Device Memory Damaged I have a Samsung S3 GT-i9300 which has an error on booting up. It goes through the Samsung splash screen then displays the following:

Device Memory Damaged
The data partition has been corrupted. You need to reset your device to factory defaults. This will erase all your
data.

I really don't want to delete the data and am looking to recover the media from the device. I'm not bothered about getting the phone working again really.
I can boot into download (ODIN) mode, but this doesnt really assist (or does it?). I can also boot into recovery mode but I get the following errors also:
E:failed to mount /data (Invalid argument) 
can't mount '/data'(Invalid argument) 
E:failed to mount /data (Invalid argument) 
E:Can't mount /data/log/recovery_log.txt

The device shows in Nautilus on my Ubuntu system but fails to mount. I can select the option to 'Apply update from ADB' and running adb devices shows as:
$ ./adb devices 
List of devices attached 
4df74280146d3071    sideload

Is this of any use to me? Is there a way I can get into the storage to salvage what's there. Can I load a custom rom without deleting everything, or if I do delete everything is there a way to recover the deleted files?
You could get the same version of your operating system as flashable zip-file for the recovery mode and flash it, or use Odin to flash a kdz-file of it. If the files you'd like to get back are not in the system folder (like music or images) there is a chance they will still be there with the flashed system. Just don't do any formatting prior to flashing!