How many bars of soap will you make?  How big a factory will you make?  How will you be able to tell if the factory is returning on its investment?

When you buy soap, will you carry a card to the soap manufacturer that says you have a need for soap and offer your ability to do something for him?  What if he's not interested in any of the stuff you like to do or have ability to do?  "Umm, I don't have a need at this time for any performance art.  Thanks for offering, though."

Money is an extremely valuable social institution.  It makes possible such wonderful things as loans, interest, measurement of return on capital, saving, and intelligent pricing (cost comparisons) in economies with vast numbers of different kinds of goods.

Most fundamentally, money is medium of "indirect exchange".  Because everyone is trading money, you can use your abilities to benefit someone who has a need for them, and in return acquire money, which you can spend on something related to your needs and not your abilities.  Transactions themselves become much simpler and less costly.  Money enormously aids the wheels of cooperation precisely because of that separation of need from ability.  Money enables people to make large investments in ways that benefit huge numbers of people without ever even meeting those people.  The investors just respond to prices--prices that are set by people negotiating as hard as they can for the best bargain they can find.  

Investment, in turn, is the main driver of productivity.  A person's productivity is mostly a function of how much has been invested in the capital goods that he uses to do his work.  With no measure of return on investment, with no meaningful prices that reflect a compromise among many people, investment would become uninformed, productivity would suffer enormously, and we'd all have a lot less means available both to satisfy our needs and to exercise our abilities constructively for others.

In summary, if money were to be replaced by [Cards], it would be a catastrophe on the scale of the Soviet Union.  Well, actually, no, because people would quickly reinvent money.  Even the Soviet Union stayed afloat mostly because of black markets.

None of this implies that [Cards] are anything less than wonderful.  They just can't replace money in large society.  

'''Therefore,'''

 * Use [Cards] in addition to money.

'''But,'''

 * This argument is based an invalid assumption, that people use Cards to arrange barter.  Barter is obsolete.  We do not encourage barter or any other form of conditional exchange.  We do things freely for one-another without asking anything in return.  A soap manufacturing company would receive free labour from the community, and provide free soap to the community.  There need not be any relationship between the set of labourers and the set of customers.  The people providing the soap would take care that no one were massively abusing their service, if that proved to be necessary.
 * Conditional exchange (of which money is a manifestation) is an extremely damaging social institution.  It makes possible such terrible things as debt, exploitation, wage-slavery, hoarding, poverty, starvation and war, to name but a few.
 * As we are abandoning the practice of conditional exchange altogether, we don't need a medium of "indirect exchange" any longer.  We can still invest our efforts into large group endeavours, which benefit multitudes of people we have never met.  People in the free software movement have been doing this for years.  Our new permaculture farm in Healesville will provide free food for thousands of people - and the free workers on the farm will not have met many of those people.
 * The act of "negotiating as hard as they can for the best bargain", with respect to car-drivers and petrol, is arguably the major cause of the current massacre in Iraq.  Bargain hunting, and being miserly, is not a good thing.
 * The main driver of productivity in the free community is enthusiasm.  We can still invest, we invest our energies into projects that seem worthwhile.  The concept of investment is not at all dependent on money.  Also, we can continue to measure and analyse the time and energies invested in a project, and the quantity of goods or services produced and consumed, without having to practice conditional exchange.  As we will be co-operating, not competing, with other producers, we need not be obsessed by productivity and profitability.  We can consider, instead, the well-being of workers and the quality of our goods.  Exploitation and built-in redundancy will be a thing of the past.
 * We do not seek to forcefully replace money with cards.  We are not interested in violent revolution!  We believe in gradual social reform or transformation.  We want to be befriend and co-operate with anyone and everyone, including wealthy capitalists, multi-national corporations, and evil dictators.  We are taking great care to make strong, decentralised systems.  The abuse of power that took place in the Soviet Union under Stalin cannot occur in a decentralised system, as no one person or small group has the power to injure the community.
 * Whether or not Cards can entirely replace money is not certain at this time.  We are not focussing on destroying money (in fact money is barely mentioned on our website).  Rather, we are creating a vibrant alternative to currency, in the spirit of LETS, but more progressive.  If many people like the alternative, and participate, money will gradually be displaced.  If people don't participate, money will persist.  I personally expect that in time, money will be relegated to historical games such as Monopoly.  We will demonstrate to our children, by playing and discussing such games, how the use of money inevitably leads to suffering.