One thing that I think is overlooked with digital is the ease of it being replicated and backed up. Paper ballots can be destroyed.

I really like the systems where there is an original easy to use paper ballot, that gets fed into a scanner for immediate counting with the ballot being stored securely in a box below the machine. It seems that the ballot could also have a scanned image stored for posterity.

At that point all the digital information can be immediately backed-up, replicated, and so on. It seems like it's the best of both worlds...