Yankadian:

I'm not an economist, but as I understand it the main problems with using currencies to assign value to things is that the central banks who produce our money mainly do so with debt - ie they print more cash than they have in reserve, and hence interest is added.

This means that the value of your $10 or £ or € is constantly falling, with every new banknote being a kind of loan with interest attached. Therefore the economy has to be constantly growing just to keep standing still.

Hence we are left with the myth of perpetual growth and the need for a country to either exploit another country's resources to grow (or stand still), or force their own workers to work ever harder. Not because it will make us happier or richer, but because we have to pay the interest on the currency.

The animated film Money as Debt about the subject is on Google Video, and Freedom to Fascism is also supposed to be good on the subject with relation to the Federal Reserve.

So while using some kind of numerical system to assign values to items and work makes sense, this doesn't have to be through central currencies - there are lots of successful community exchanges, like the Talents system from the South Africa New Economics Network - they even have a shop and exchange rates with other systems around the world.