As a professional, digital asset management is crucial!
Here is my process:
Prior to ever erasing a card....
0. Download to computer
1. Back up to external drive
2. Back up to Dvd
Then I make contact sheets and take a screen grab of the "hero" image from the shoot and make another contact sheet with the single 'hero image" (best shot from shoot)
to log which disk the files are burned to.
Always always always back up, you never know when you ll lose data!
Hope I helped!
I've got an iOmega 1TB USB Hard Drive. Everything gets copied to the HD and only then do I erase the Card. When I get low on space, it gets burned to DVD.