I'm keeping 3 copies with one off-site.
I import to my MBP and make a backup right then to a different temporary drive. I then backup my MBP as well before formatting the CF or SD cards. This leaves three copies (MBP, external drive, and MBP backup on separate external).
When I'm finished with the edits, I transfer the images to my 'archive', a RAID-1 FireWire drive, and also to an external drive that I keep off-site.
1: Take pics! CF/SD - one copy at this point (or two with the dual slot in the 5DM3 or similar)
2: Import to computer and make external backup - 3 copies at this point (CF card, computer, external drive)
3: Backup computer to separate drive - 4 copies at this point (CF, computer, external, different external)
4: Format CF/SD cards - 3 copies
5: Edit images
6: Move images from computer to RAID drive when finished and also copy images to permanent external drive used for storage. You can then reuse the temporary drives and computer backup drives as they fill. This leaves you with 3 copies (two on the RAID and one permanent external that is kept off-site).