Did Ben Bernanke just ok'd the use of Bitcoin?
Not quite. Watch the video again. He chose his words very carefully.
Its also perfectly fine to hold other currencies, euros, yen or whatever else
Youre allowed to "hold" alternative currencies, but he didnt say you can issue, circulate, transmit, transact or trade in alternative currencies. Bernard Von Nothaus found out the hard way, when he issued Liberty Dollars, that the government has a very strong dislike of alternative currencies. He was charged with terrorism offences.
No, the issue with Liberty Dollars was that they were called dollars and looked a bit like US dollars. There's absolutely nothing illegal in the US (and clearly not in other jurisdictions) with using any alternate currencies at all. Legal tender means that, where there is a debt and one party wants to settle it in US dollars, the other party cannot refuse and claim the debt is unsettled... that's all.
This entire argument about the legality of Bitcoin is nothing but a wild goose chase.