Wanted to share a bit about buying tickets in pesos...
We just bought two RT tickets (AR > US) with United online and went to their local office to pay for it in pesos yesterday.
No issues, the online checkout process adds the 35% to the total automatically (still, we saved just over USD $700 with the blue rate).
While at their office, they did ask me (as the ticket buyer) for my CUIT/CUIL and home address here in BA, which I thought was a bit odd. Then they did the same with another group of locals who were buying tickets there. The agent explained to us that as of yesterday (Jan. 16 2014), for anyone paying in cash (though it may likely apply to card purchases as well), the government is now requiring them to record the purchaser's name, DNI, CUIT/CUIL, local address, razon social, etc. So the agents now have a new online form to fill out when you pay that requires them to collect this info. No word on why, just seems to be more of that "tracking" the government and AFIP seem to be doing lately.
BTW, at the office, they can only accept $10k pesos cash per traveler, so if your total is more than that, they'll direct you to a Citibank 2 blocks away to make a deposit into their account (we did this).