I arrived in early May 06 with a return ticket for late September 06 (obviously well beyond the routine 90 days granted upon entry). No one said anything about it: neither the airline or Argentine migraciones as I entered. In early August I got the 90 day extension (100 pesos) at prorrogas de permanencia at the office of migraciones, but I did so only because I was ready to apply for a one year visa. I've never heard of anyone having a serious problem for overstaying a tourist visa...just the 50 peso fine....and no trouble if and when they want to come back.