Incidentally, Argentina must do this because they have no access to foreign capital markets due to things like seizure of YPF, devaluation of the peso in 2001, and failure to pay back the lenders they still owe, etc. Foreign currency reserves just keep dwindling. As China slows down and demand for soybeans drops, Argentina is really, really going to have a hard time. So though it seems crazy there is some "reason" for it (I'm not trying to make a political comment, I personally think it's crazy and they should radically open the market, but my point is that it's not exclusively xenophobia that is driving this policy).
Unfortunately the policy just pushes the trade to the black market. One of the interesting things here is that if you need pesos, and you have some access to USD, you make an instant 20-25% on your money. The "black market" (they call it "blue" here because it seems nicer) continues to diverge. If you're a hobbyist economist like myself, it's really fascinating to watch market risk priced into a currency in realtime as seen by the "blue"-vs-official rate spread.