Digital Coin idea is based on technology in development at
http://www.maidsafe.netYou can keep tabs on their progress, ask questions or invest!
In my proposal I assumed bottom-up implementation. DC would be one option among several for local alternative currencies.
If adopted top-down, ie. by governments, then government could print paper "cash" as now.
That said, there are examples of private paper currencies.
In Canada the most universal is Canadian Tire Money
http://corp.canadiantire.ca/EN/Media/FactsAndStats/Pages/CanadianTireMoney.aspxNear where I live is Salt Spring Island
http://www.saltspringdollars.com/Personally I think it would be better if only government issued paper currency and guaranteed its value as ONE PC for payment of taxes.
However in a chaos collapse situation we would have to make it up as we go along with whatever is available to us. In "the Essence of Money" Anton cuts up a unique piece of fabric into little pieces and attaches a signed IOU. The IOU plus the fabric piece are required for redemption.
For example, at a weekly market, each seller could issue IOUs attached to some piece of fabric stamped with a unique potato block print. Make a new potato pattern each week to prevent counterfeiting.
Paul