A new economy? a new currency? a new decentralized banking?

Total fucking bullshit.

Bitcoin is just another huge pyramid scheme!

The beauty of Bitcoin is that it may provoke people into thinking exactly what they want their currency to be. i.e. a stable store of value and a means of exchanging labour for goods and services. Due to speculation and lack of uptake by vendors, Bitcoin currently fails both these pretty basic requirements but is the dollar/pound/yen/yuan that much better? ;-)

And fiat currencies aren't +Terrence Miao ?

The jury is still out on whether it will be stable long term but it is definitely not a pyramid scheme.  It is a currency based on producing digital hashes that take a certain amount of computation to produce at the same time as protecting the system from hacks and forgeries.  But just because they take resources to produce doesn't mean they have any intrinsic value and leads people to speculate on what their "true" value is.  Speculation leads to bubbles and large changes in exchange rate which undermines its use as currency.  
I think its main attraction is anonymity in addition to it being a great vehicle for discussing what currency really is. 

In U.S. it's called buck, in U.K. is quid, in Canada is loonie, in Down Under is moolah ...

On Greenback says "In God We Trust"; on Renminbi has Chairman Mao's portrait as the God bless; on Australian $20 note it says: "This Australian note is legal tender throughout Australia and its territories", and it's signed by the Governor of the Reserve Bank. Both of them are recognizable, acceptable, exchangeable around world.

What are Bitcoin and other virtual currency backed and guaranteed?