Today that transaction would be worth nearly $4 million, probably making those the most expensive pizzas in the history of the world.

But back then it was considered revolutionary to trade a 'digital' currency, something that few people really understood at the time, for a real product.

People are still skeptical of digital currency. But the concept itself is not so esoteric.

As Jim Rickards reminded me some time ago, MOST currencies are digital, even the US dollar.

The Federal Reserve's estimate of US dollar money supply is $12.1 trillion; yet only about 10% of that is physical cash in circulation.