Well...not quite double for free. Bitcoin regulation is well on its way and uncle sam (or other tax authority) will want to capture your gains on that sale at $720. Bitcoin will be quite traceable and I suspect audits will come down the line for anyone reporting gains in bitcoins in 5 years or so. So you'll get double coins but probably a small tax bill to make up for it.

It's not all bad news though. Ask your landlord (if you have one, for instance) if he/she will accept rent in bitcoins, and buy the difference of bitcoins in your rent. That way, your "new" bitcoins will get taxed against that rate, instead of the cheaper rate. I think that's excellent motivation to spur the adoption of bitcoins