Fast salt - use salt shakers in Argentina with extreme caution. Their normal-looking shakers release ultra fine salt from ultra big holes.
Small feet - I tried to buy a pair of Merrell all-weather mocs to hike around Iguazu Falls, and discovered that my feet, which are size 9, are freakishly larger by Argentine standards. I was laughed out of two shoe stores (they tried to convince me to wear 8s at both. "They stretch!")
To drink or not to drink the water - we use tap water to brush our teeth, and we haven't had any problems. We keep bottled water for drinking, and always order a bottle of agua con gas in restaurants. Even the locals seem to prefer bottled water. I don't think the tap water is dangerous, but if you're on vacation for only a week or two, it's not worth the digestive adjustment period.
Traffic lanes are mere suggestions. On a four lane street, it's common to see six or seven improvised lanes of cars. The cars are small, and they weave through traffic with so little room to spare that you feel you could be crushed from either direction. It's really terrifying, but it works. Traffic flows relatively smoothly, and most of the cars have seatbelts.
Cars are different - The ones we see in Buenos Aires are primarily Renault, Peugeot, VW, Ford, and Chevy. We've seen a handful of Mercedes (mostly tiny A160) and BMWs, and a lone Volvo wagon. Other than a handful of Honda Fits and a lone Toyota Corolla, we haven't seen many Japanese cars at all. The vast majority of cars seem to have manual transmissions, and we haven't seen a single airbag in any car in Buenos Aires. We take half a dozen cabs every day, so we've been in a lot of cars!
Two yellow lights - in Buenos Aires, traffic lights turn yellow before they turn red, but also before they turn green. My observation is that they blow they yellow light that comes before the green one regularly, but they seem to heed yellow before red. I guess you have to heed one or the other if you want to stay alive here.
Table charges - many restaurants charge a small cover fee for each person at the table. They range from about 2 pesos to 6 pesos, or about $0.66 to $2.00. This is NOT a tip; it's the restaurant's "cover charge." If it sounds like a scam, consider this: restaurants do not ever-- ever-- rush you here. You can order a cappuccino, and sit at a table all night. At one restaurant, Señor Telmo, we eavesdropped as a woman at a neighboring table tried to dispute the charge. Her husband had lunch, but all she'd had was a cup of coffee. She pleaded for ten minutes for them to drop the 2 peso charge, but the restaurant adamantly refused. Some of the higher end restaurants don't have a table charge, but most do. We've spent 250 pesos on dinner, and still been hit with the table charge. In Uruguay, our check also had a charge (that worked out to less than 50 cents per person) for the musicians who played during dinner.
Tips are appreciated here, but they're smaller. In restaurants, a tip is never guaranteed, but servers expect about 10%. Quite honestly, the service level rarely warrants more. The server takes your order, and brings your stuff to the table. You flag him down if you need anything else. You flag him down for the check. You pour your own wine and water, and you grind your own pepper. Not all restaurants accept credit cards, but even among the ones that do, you can't leave a tip on the card. Be prepared to leave cash. We've had a couple of experiences (notably at El Establo) where service was outstanding, and on those occasions, we've tipped 20-25%.
More on tipping - Porteños generally give taxi drivers no tips at all, or small tips by rounding up to the next peso on cab fare. We've left small, 1-2 peso tips for the most part. We've deviated from this local practice when a driver has gone out of his way for us. For example, the driver Lorena called to take us to Chacarita made multiple stops. We tipped him 20%. Our B&B's housekeeper and breakfast cook, Norma, has taken very good care of us. We leave what's considered a good tip (by local standards) for her every day-- 5 pesos, or about $1.67. It takes very little money by American standards to reward good service here, and the locals are truly grateful. We plan to leave a significantly larger, American style tip for Norma on our last day.