Well, not extreme culture shock, but it's amazing how quickly we noticed the sheer overwhelming number of options we have, as Americans, in nearly anything we could possibly want. As an example, when I was looking through the bookstores in the Miami airport, I was absolutely amazed by the insane number of magazines that I could have bought. Obviously, it's not like I didn't know that before, but after a couple of weeks in which my 2 primary English language options were "take it" or "leave it," it was certainly pretty shocking to see 14 different lawn care magazines after several weeks of seeing nothing in English.
The same thing was true in the realm of airport restaurants, although we didn't get to really enjoy our choices because for whatever reason, MIA keeps most of their restaurants before you get to security, and since you can't take drinks through, it's not a very layover-friendly airport. While Argentina and Chile have some franchises, they certainly are nowhere near the state of proliferation that they are in North America, although it's possible that Chile in particular has more fast-food restaurants than even the US does. Chile's, however, aren't generally franchises, other than the few McD's in Santiago.
On a completely unrelated note, after loading the page so much on South American computers, my blog's default language is now Spanish.