I wouldn't technically consider Bitcoin as a global currency, as it still isn't very widely known. Countries tend to like to have total control of their coin, and since Bitcoin is a P2P currency, their only kind of control is having a huge share of the 21 million coins. I really don't think it will become a global currency, as it is quite an unstable little thing.
Countries can't stop innovation. Bitcoin may not become a global currency but it will be used by hundreds of millions at least and when there is such an adoption, the price will stabilize as well.