As far as I'm concerned, if the Bitcoin to fiat exchange rate can stabilize sufficiently, then it becomes a better online currency that any single nations currency at the moment.

Better because of reduced fraud and reduced transaction fees.

I don't see any fundamental reason why this can't happen with a non-government crypto currency, but it will take some time... and there will be a lot of booms and busts along the way.

The biggest risk is sadly the US government declaring it illegal.