I work with computers all day long, so I know what could happen to them when fate decides to strike. That's why I back up my originals and processed files to DVD periodically.
But the old saying 'haste makes waste' is still alive and true. I just got back from a shoot and I had a 1 gig card to process, but I was nearly out of space in my hard drive partition. So, I cut the first of four DVD's worth of files from my new 20D camera. When the first DVD was cut, I popped it out of the reader and put it back in to force the computer to re-read the DVD. This would ensure I had a valid backup before I deleted the directories.
My mistake came when I negelected to perform this extra step after burning the successive three DVD's before deleting the directories. And wouldn't you know it, two of the remaining three DVD's had encountered a 'soft error' in the boot sector of the DVD. Apparently this was not enough to fail the burn, since it appears to be due to a defect in the DVD media itself. I had two bad DVD's in my 30-pack bundle AND I had deleted half of my first pictures from my new 20D camera!!!
So, the moral of this story is to always double check your DVD/cd backup BEFORE deleting your directories! 

