You could just put your transaction in the newspaper to get the ordering guarantees that the block chain provides, though without the crypto. A Bitcoin-like system is probably not possible: A simplified proof-of-work could be done by hand, I suppose, but cryptographic signing is more difficult. The cost of transaction and block verification would be especially limiting.

Time per confirmation is limited by the latency between miners. If all miners are located in a small area and are using couriers, a few confirmations per day could be supported.

Unless the proof-of-work is massively easier for humans than computers, the system could not withstand an attack by computers.

Look to Captchas for inspiration. Basically anything a human can do easily which a computer cannot.

The proof-of-work needs to be easily verifiable. I don't think anything exists yet.

The question of human-performable cryptographic signing (and while not necessary for bitcoin, encryption) is also an interesting one that I've batted around casually without success.  Making use of an external visual aid seems quite promising but the important thing is coming up with a method not revealed to an adversary who can see where you're looking.  If I ever get the kinks figured out I would seriously consider getting the visual aid as a tattoo.

Sounds good. They have those on Newegg, right?

+1