Just returned from EZE last week and had a blast! I jumpseated on UA out of IAD with no problems and got upgraded to Business. The return flights were more problematic... UA, DL and CO all depart EZE within an hour of each other. However, UA was delayed for over 6 hours, DL was weight-restricted so CO took me to IAH with no problems. If you jumpseat on CO, ask for Jorge (I think he's the supervisor). Great guy and took care of my jumpseat request. Once there, I stayed at the Telmotango Hostel in San Telmo - $17 USD per night for a decent place in a decent area. The city was lots of fun and very cheap but quite dirty. Have fun and PM me with more questions! Good luck.