I'm afraid of Bitcoin becoming the world's only currency. Someone with enough computing power can massively game the system. I'm not saying that that can't happen with today's government driven currencies, but that there are at least other options right now. Maybe we shouldn't all switch to Bitcoin.
I'd be afraid of it becoming even a common currency. The problem is bitcoin does not encourage economic growth. It is smarter to hold then to spend. In a good currency, the demand for the money itself should not cause prices to fluctuate.
I think this could be solved if instead of the difficulty target being determined based on a steady release, was instead determined in someway based on the quantity theory of money (MV = PY) so as there is greater demand for coins more coins would be produced, and the opposite, when we have enough coins, less are produced.
