Practicalities aside – and hypothetically speaking – how would it work out?

….Would global economics simply cease to exist?

….Would it be akin to some form of communism?

….Which country would be 'richest' – and how?

….Or would it foster global peace, love and harmony forevermore?

Maybe the times of the roman empire might shed some light, I know it wasn't total but it covered a large percentage of the planet.

Nothing would happen, we virtually have one currency now – its called money. All we have done is sub divide money into our own version of it.

A bit like the Euro in Europe – local variations of the same money. They still have quite different economies – look at the difference between Italy and Germany for example.

Until you smooth out the differences in rescources/abilities/labour markets etc it wont matter if your all using the same currency.

All animals all equal. But some are more equal than others.

They are not all equal, some ride singlespeeds 🙂

I like Trimix's answer – the differences between the various forms of capitalism we see in Europe is huge and is itself enough of an argument for the UK not to join the Euro.
France and Germany are what are known as 'alliance capitalisms' whereas the UK follows the so called 'anglo saxon model'. The UK's form of capitalism is closely aligned with the US, while France and Germany look a little more like Japan (more so Germany; France is what is known more technically as a dirigeste, which means a state coordinated economy, which is not the same as communism, which is a state controlled economy).
Alliance capitalism place greater emphasis on economic cooperation and commitment, for example between the unions and employers, between companies and their owners, which are typically banks. In the Anglo Saxon model, owners are fragmented, arms length shareholders who have little involvement in the way companies are run; union relations are typically adversarial and there is little if any customer loyalty.
Neither is better or worse, it's just different but both have strengths and weaknesses. For example, alliance economies tend to build excellent cars (Germany & Japan) because this skill needs process refinement and that is supported by greater commitment between employer/employee for example. the Anglo Saxon model is better at radical innovation because that is propagated by a highly mobile, flexible work force that moves around a lot and thus gives rise to exchanges in ideas.

Well summed up 'geetee 1972'. Money is just a tool, its how you use the tool that matters.

In the pub one night myself and some friends proposed a new global currency. We call it the quid, and anything cost a quid. A house was a quid, a car was a quid, a pint was a quid. We reasoned that it didn't matter what a house costs if they all cost the same, might as well be 1 quid as you only need one, we then did lots of other reasoning, but as we'd decided that we definately needed more than one pint, I've forgetten it all. I'm certain though that it was uncontrovertible brilliance.

Skidartist, that sounds like the other theory where you make leaves money. Then everyone will be as rich as they like just by picking up leaves. Great, all millionaires.

Or the one about everyone haveing the same amount of money – or the one about everyone haveing the same choice of things to spend it on.

I reckon either staying drunk, or winning the lottery is the best way forward. (or marrying a rich woman)