Market chaos leads to meltdowns. If it is restricted to the pre-modern or emerging market economies and only extremely limited, it might be useful. Any capital controls dealing with a major country would be anathema. Can't imagine that the Secretary of Treasury and Co. wouldn't warn emerging economies of the long-term danger of restricting money flows. This happens with some regularity.
Problem is to time the easing of controls to allow orderly transition without economic disruption.
Might be very wise in light of Southeast Asia's slow recovery. Countries traditionally resistant to dollarization acquiesce out of desperation. It's just the de facto reliance upon the US dollar as currency of choice in those countries where the local unit is worthless. Settlement of financial transactions This could dramatically reduce confidence. The settlement functions regarding Y2K in the recent Securities Industry Test went without problems.