And they do (have to) enforce it as well now.
Left Las Americas 2 weeks ago and had overstayed one day (plane schedules don't really take the overstay chart into account
). Had to pay 2500 pesos at the cashiers window and got a receipt. I joked to the woman officer if they were not going to arrest me for overstaying so I could stay longer and she said no
. Then she said something interesting: She said next time when you come, instead of buying the tourist card on entry ask for the 90 day visa and that will only cost you 2.000 pesos. So it seems that this rumored 90 day visa does exist (or at least this customs officer thought it did).